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C# vs. Java for game development

I've been mostly programming in C++ as of late, but to be honest I think I need something else I could use. C++ being quite low level requires much more time to make things. It would be nice to know another popular language that is easier to code in. If I were to use C# I'd probably use XNA with it as well, however I'm not quite sure about Java. I know that Java is more cross-platform than C# and that C# is pretty much in Microsoft's pocket however that doesn't bother me. I'm mostly gunning for 2D ASCII/Sprite games as opposed to 3D, however 3D is indeed something I'll eventually move on to.
I want to know what the Stack-overflow community thinks.

XNA is really easy to use for 2D games. Not only does XNA give you content pipeline management within Visual Studio, which makes managing the entire build job quite easy, the framework also sets up a basic game loop and gives you the building blocks to get started. There are plenty of getting started guides and even a growing pile of books on XNA.
XNA works with the free version of Visual Studio and XNA runs on Windows Phone and the Xbox 360 (unfortunately deploying to either of these platforms requires a $100 a year license from MS).
I am sure there are good libraries for Java as well, but I can't give you any details.

I know this was answered quite a long time ago, but on the Java side of things you could have easily used libGDX. It is totally open source and simple to learn the basics. It supports Android, IOS, Desktop (Mac, Windows, and Linux via the JVM), and HTML5. The only (small) learning curb is figuring out how to set a libGDX project up via the Eclipse GUI, but if you are a command line person (and most people here are) then this is one of the most qualified frameworks out there.

MonoTouch, the future of MonoTouch and whether I should use it for iPhone apps (instead of objective-C)

I've decided to start writing an iPhone app and coming from a c# background, I thought I'd start developing it with mono.
Though this question may be subjective, I'd love some guidance from you.
Is it safe to develop my app using this technology, or should I buy some books and start learning objective C?
I know Adobe were going to release a feature that allows you to build iPhone apps using Flash CS5, but this didn't last long.
I appreciate your feedback.
Marko

Monotouch is doing a great job of keeping up to date (usually within 24 hours of api updates) so just saying you have no idea about xyz but you know abc is much better than it is a bit silly. Monotouch has some serious advantages over obj c - for instance obj c has only been updated something like twice in the last twenty years!! expect good XML, regex, Http support? Think again. Linq in Obj c? never. Good OS community? Not likely. There's plenty of reasons to use MT, aside from C# being a far superior language. Being able to re-use a good percentage of your code in MonoDroid is one. Though there is word that apple are creating a new language - I'm not holding out too much hope for it. We'll see I guess.
I learned Obj C before getting into MT and the reason I went with MT is that using Obj C is like stepping back into the 90s. It just doesn't have any modern language features and is too far behind the curve. Create your bleeding edge apps with their archaic langauge? Thanks but no thanks.

None of us except people who work very closely with the OS and the App store policy in Apple would know whether it is "safe" to develop apps using this technology. Apple can say no anytime in the future, but we don't know. What we know is that all the compiled code has to be in C, C++, or Obj-C. However there's one catch: In some cases you can run interpreted languages.
If I were you, I'd go with Objective-C. We know that Apple supports it fully, it's been in there for almost 20 years. It's not that hard to learn since you know C#. I came from C++/C and it took me about a month or so to learn half of the frameworks. There are many other frameworks which I didn't learn because they're not applicable in my apps (such as accelerators, GPS, OpenGL ES, etc). You probably can get away with this too.
Once again, there's also another way: build it with HTML5. However that way you'd have to consider what your app'll do when it's opened with Safari desktop, Firefox, IE, etc.

The iPhone dev agreement is pretty clear that C# is not an accepted technology for developing iPhone apps. Regardless, Monotouch apps have still been accepted to the app store to date without any problems. My suggestion is to keep in touch with the Monotouch forums to see what their stance is on this issue and make your decision based on that. The long term safe bet is to go learn Objective-C.

Recently Apple changed the clause relating to the third party development tools now stating that if you have prior approval you can use them. I haven't seen any official word that Mono will be allowed though.
If you are coming from a c# background I would highly recommend learning Obj-C because it always helps knowing another language and you could pick it up reasonably easily. Have a look at the stanford University iPhone lectures, they were the best resource when I was learning.
Although I haven't personally used C# or Mono, the iOS SDK once you get to know it has some really great work behind it making it both easy and powerful once you get used to it and I would be surprised if Mono took advantage of it all.

I think it's important to learn the language the frameworks for your platform of choice were written in. Then you can understand more why the frameworks are the way they are, and often anticipate behavior or API calls just based on knowing what is typical for the language and framework.
On top of that there is now a ton of support for blocks across the API (iOS4 and on only), which may take some time to be incorporated into MonoTouch. Overlay frameworks are always a step behind the base platform so it's nicer to be using the frameworks directly.

It's now been months since the Flash debacle and Monotouch and Unity are still rocking along.
As developers in a .NET shop we're looking at expanding into iOS development. After prototyping some fairly basic stuff in Objective-C, We're 100% committed to using Monotouch, it's worth every penny.

Quickest (Easiest) GUI MFC or C# or QT or?

I have just finished my first real commercial application written in C++ / MFC.
The application consisted of agent installed on users workstations which in turn was controlled from a GUI Application on an administrators workstation. I choose C++ / MFC for these reasons.
Because I didn't know C#
Because I was not sure how long it would take for me to become as productive in a new lanuage
Because I did not want the hassle of installing the .NET runtime on workstations some of which might be W2K.
Now I am thinking of my second application which will again consist of an agent & a GUI Application. I am happy to continue on the same track with the agent for the reasons above but the GUI application will be much more complicated then the first. The first GUI app took a very long time to develop, was torturous and looked out of date even though it was freshly made.
Should I just bite the bullet with .net c# or look into something like QT.
TIA.

If you want really fast results, use .NET WinForms. Nothing beats the speed of putting together a GUI app and filling it with life, except maybe Delphi. The C# language and the .NET Base Class Library will also give you a huge productivity gain, even over the already great Qt framework. If you stick to the basic Windows Forms controls, it will even run on Mono.
WPF is even more productive once you're used to it, but getting used to it takes way more time than for Windows Forms.

.NET C# is a very good choice for GUI applications more generally. It's simple, to-the-point and there are vast resources on the internet.
The only thing against it I can think of, is platform compatibility, but if you're limiting yourself to C++/MFC, that shouldn't be a concern to you.
Even if you want to go platform-independent some time later, you can make a separate Gtk in .NET on Linux (Mono, the open-source .NET framework). Heck, there's even a Cocoa (Mac OS X) binding, I just don't know how mature it is. Furthermore Windows Forms is largely supported in Mono already... it really surprised me how mature it is when I was trying it out, although my primary experience with C# is on Windows.
For GUI application, you won't regret using C#. Even if you want to go cross-platform, and certainly not if you intend to only target Windows clients.

C# will almost definitely make you more productive!

Delphi. Produces stand-alone Windows executables which will work fine on Win2K (best OS Microsoft ever produced - this post is being written on it). Only disadvantage is Object Pascal, but if you know C++ it's very easy to pick up - and its was designed buy the guy who designed C#. The IDE is several orders of magnitude more productive than MFC with VS.

I've done them all - a monkey can use C#, it's all drag and drop interfacing and public accessors. I wouldn't wish using MFC upon my worst enemy, and QT just wasn't as intuitive as C# for me. It's also really easy to make C# look nice. Difficult things like changing colors and flashing controls are trivial in C#. It also has built in styles to use. I use it professionally daily. The only time I use C++ is if I'm programming a server where every microsecond counts.

The first question would be exactly what caused the difficulty in developing the GUI with MFC. Was it inherent to MFC, or what it because you were learning something new, and didn't really know what you were doing? To put it slightly differently, if you had to do it again today, how would the difficulty compare?
Make no mistake about it -- MFC is an old design with far more than its share of problems, shortcoming and design flaws. .NET is a lot newer, but has far more than its share of problems, shortcoming and design flaws as well.
Along with that, .NET is just plain huge. It's reasonably well organized, which helps, but it still takes quite a while to digest the sheer volume of information necessary to use it well. Likewise, while C# (for the most obvious example) is a perfectly decent language, learning to use it well isn't an overnight task either. This is probably a smaller issue though: C# doesn't really have many new concepts compared to C++. Just for example, a competent C++ programmer can easily read C# almost immediately, and while he may not use it optimally, can also write bits of C# immediately as well.

on which platform will your second app run on?
if it's XP and up i'll suggest C# / WinForms / GDI.

C# isn't that hard to adapt to, and there are literally a ton of examples online, and great books (the Head First one caught my eye as you can code a nethack clone and other fun projects). I've had to transition from C++ to C# myself, and it wasn't that rough at all (in fact it seemed like a pretty easy transition), and allowed me to rapidly prototype.
Good luck!

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After sitting through a session today on Mono at a local .Net event, the use of MonoTouch was 'touched' upon as an alternative for iPhone development. Being very comfortable in C# and .Net, it seems like an appealing option, despite some of the quirkiness of the Mono stack. However, since MonoTouch costs $400, I'm somewhat torn on if this is the way to go for iPhone development.
Anyone have an experience developing with MonoTouch and Objective-C, and if so is developing with MonoTouch that much simpler and quicker than learning Objective-C, and in turn worth the $400?

I've seen this question (and variations on it) a lot lately. What amazes me is how often people respond, but how few answer.
I have my preferences (I enjoy both stacks), but this is where most "answers" start to go wrong. It shouldn't be about what I want (or what anybody else wants).
Here's how I'd go about determining the value of MonoTouch - I can't be objective, obviously, but I think this is pretty zealotry-free:
Is this for fun or business? If you wanted to get into consulting in this area, you could make your $399 back very quickly.
Do you want to learn the platform inside-out, or do you "just" want to write apps for it?
Do you like .Net enough that using a different dev stack would take the fun out of it for you? Again, I like both stacks (Apple and Mono), but for me MonoTouch makes the experience that much more fun. I haven't stopped using Apple's tools, but that's mainly because I really do enjoy both stacks. I love the iPhone, and I love .Net. In that case, for me, MonoTouch was a no-brainer.
Do you feel comfortable working with C? I don't mean Objective-C, but C - it matters because Objective-C is C. It's a nice, fancy, friendly OO version, but if pointers give you the heebie-jeebies, MonoTouch is your friend. And don't listen to the naysayers who think you're a dev wuss if it happens that you don't like pointers (or C, etc.). I used to walk around with a copy of the IBM ROM BIOS Pocket Reference, and when I was writing assembly and forcing my computer into funny video modes and writing my own font rendering bits for them and (admittedly trashy) windowing systems, I didn't think the QuickBasic devs were wusses. I was a QuickBasic dev (in addition to the rest). Never give in to nerd machismo. If you don't like C, and if you don't like pointers, and if you want to stay as far away from manual memory management as possible (and, to be fair, it's not bad at all in ObjC), then... MonoTouch. And don't take any guff for it.
Would you like to target users or businesses? It doesn't matter much to me, but there are still people out there on Edge, and the fact is: you can create a far smaller download package if you use Apple's stack. I've been playing around with MonoTouch, and I have a decent little app going that, once compressed, gets down to about 2.7 MB (when submitting your app for distribution, you zip it - when apps are downloaded from the store, they're zipped - so when figuring out if your app is going to come in under the 10MB OTA limit, zip the sucker first - you WILL be pleasantly surprised with MonoTouch). But, MT happiness aside, half a meg vs. nearly three (for example) is something that might be important to you if you're targeting end users. If you're thinking of enterprise work, a few MB won't matter at all. And, just to be clear - I'm going to be submitting a MT-based app to the store soonishly, and I have no problem whatsoever with the size. Doesn't bother me at all. But if that's something that would concern you, then Apple's stack wins this one.
Doing any XML work? MonoTouch. Period.
String manipulation? Date manipulation? A million other little things we've gotten used to with .Net's everything-AND-the-kitchen-sink frameworks? MonoTouch.
Web services? MonoTouch.
Syntactically, they both have their advantages. Objective-C tends to be more verbose where you have to write it. You'll find yourself writing code with C# you wouldn't have to write with ObjC, but it goes both ways. This particular topic could fill a book. I prefer C# syntax, but after getting over my initial this-is-otherworldly reaction to Objective-C, I've learned to enjoy it quite a bit. I make fun of it a bit in talks (it is weird for devs who're used to C#/Java/etc.), but the truth is that I have an Objective-C shaped spot in my heart that makes me happy.
Do you plan to use Interface Builder? Because, even in this early version, I find myself doing far less work to build my UIs with IB and then using them in code. It feels like entire steps are missing from the Objective-C/IB way of doing things, and I'm pretty sure it's because entire steps are missing from the Objective-C/IB way of doing things. So far, and I don't think I've sufficiently tested, but so far, MonoTouch is the winner here for how much less work you have to do.
Do you think it's fun to learn new languages and platforms? If so, the iPhone has a lot to offer, and Apple's stack will likely get you out of your comfort-zone - which, for some devs, is fun (Hi - I'm one of those devs - I joke about it and give Apple a hard time, but I've had a lot of fun learning iPhone development through Apple's tools).
There are so many things to consider. Value is so abstract. If we're talking about cost and whether it's worth it, the answer comes down to my first bullet item: if this is for business, and if you can get the work, you'll make your money right back.
So... that's about as objective as I can be. This is a short list of what you might ask yourself, but it's a starting point.
Personally (let's drop the objectivity for a moment), I love and use both. And I'm glad I learned the Apple stack first. It was easier for me to get up and running with MonoTouch when I already knew my way around Apple's world. As others have said, you're still going to be working with CocoaTouch - it's just going to be in a .Net-ized environment.
But there's more than that. The people who haven't used MonoTouch tend to stop there - "It's a wrapper blah blah blah" - that's not MonoTouch.
MonoTouch gives you access to what CocoaTouch has to offer while also giving you access to what (a subset of) .Net has to offer, an IDE some people feel more comfortable with (I'm one of them), better integration with Interface Builder, and although you don't get to completely forget about memory-management, you get a nice degree of leeway.
If you aren't sure, grab Apple's stack (it's free), and grab the MonoTouch eval stack (it's free). Until you join Apple's dev program, both will only run against the simulator, but that's enough to help you figure out if you vastly prefer one to the other, and possible whether MonoTouch is, for you, worth the $399.
And don't listen to the zealots - they tend to be the ones who haven't used the technology they're railing against :)

There is a lot of hearsay in this post from developers that have not tried MonoTouch and Objective-C. It seems to be mostly be Objective-C developers that have never tried MonoTouch.
I am obviously biased, but you can check out what the MonoTouch community has been up to in:
http://xamarin.com
There you will find several articles from developers that have developed in both Objective-C and C#.

So, my answer to a previous similar question is to learn Objective-C. (Also, don't forget about debugging support)
This will probably offend some but to
be honest, if you are going to do any
serious development, you should learn
Objective-C. Not knowing Objective-C
in iPhone development will just be a
hindrance. You won't be able to
understand many examples; you have to
deal with the quirks of Mono whereas
if you had a working knowledge of
Objective-C you could get a lot more
out of the platform documentation.
Personally, I don't understand the
position that says increasing the
amount of information you need in
favor of using Mono over the
platform's native language. It seems
somewhat counterproductive to me. I
think if this is a very expensive
proposition (learning a new language)
then it may be worthwhile spending
some time on fundamental programming
concepts so that learning new
languages is a fairly cheap
proposition.
Another user also wrote this:
Monotouch is easier for you now. But harder later.
For example, what happens when new seeds come out you need to test against but break MonoTouch for some reason?
By sticking with Mono, any time you are looking up resources for frameworks you have to translate mentally into how you are going to use them with Mono. Your app binaries will be larger, your development time not that much faster after a few months into Objective-C, and other app developers will have that much more of an advantage over you because they are using the native platform.
Another consideration is that you are looking to use C# because you are more familiar with the language than Objective-C. But the vast majority of the learning curve for the iPhone is not Objective-C, it is the frameworks - which you will have to call into with C# as well.
For any platform, you should use the platform that directly expresses the design philosophy of that platform - on the iPhone, that is Objective-C. Think about this from the reverse angle, if a Linux developer used to programming in GTK wanted to write Windows apps would you seriously recommend that they not use C# and stick to GTK because it was "easier" for them to do so?

Using Mono is not a crutch. There are many things that it adds to the iPhone OS. LINQ, WCF, sharable code between a Silverlight app, an ASP.NET page, a WPF app, a Windows Form app, and there's also mono for Android and it will work for Windows Mobile as well.
So, you can spend a bunch of time writing Objective-C (You'll see from many studies where the exact same sample code in C# is significantly less to write than OC) and then DUPLICATE it all for other platforms. For me, I chose MonoTouch because the Cloud App I'm writing will have many interfaces, the iPhone being only one of them. Having WCF data streaming from the cloud to MonoTouch app is insanely simple. I have core libraries that are shared among the various platforms and then only need to write a simple presentation layer for the iPhone/WinMobile/Android/SilverLight/WPF/ASP.NET deployments. Recreating it all in Objective-C would be an enormous waste of time both for initial dev and maintenance as the product continues to move forward since all functionality would have to be replicated rather than reused.
The people who are insulting MonoTouch or insinuating that users of it need a crutch are lacking the Big Picture of what it means to have the .NET framework at your fingertips and maybe don't understand proper separation of logic from presentation done in a way that can be reused across platforms and devices.
Objective-C is interesting and very different from many common languages. I like a challenge and learning different approaches... but not when doing so impedes my progress or creates unnecessary re-coding. There are some really great things about the iPhone SDK framework, but all that greatness is fully supported with MonoTouch and cuts out all the manual memory management, reduces the amount of code required to perform the same tasks, allows me to reuse my assemblies, and keeps my options open to be able to move to other devices and platforms.

I switched. Monotouch let's me write apps at least 3-4 times as fast (4 apps per month compared to my old 1 per month in Obj C)
Lots less typing.
Just my experience.

If this is the only iPhone app you will ever develop, and you also have zero interest in developing Mac applications, ever, then MonoTouch is probably worth the cost.
If you think you'll ever develop more iPhone apps, or will ever want to do some Mac native development, it's probably worth it to learn Objective-C and the associated frameworks. Plus, if you're the type of programmer that enjoys learning new things, it's a fun new paradigm to study.

Personally I think you'll have a better time just learning Objective-C.
In short:
"Learning Objective-C" is not a daunting as you might think, you may even enjoy it after just the first few weeks
You are already familiar with the "C style" syntax with lots of *&(){}; everywhere
Apple has done a very good job of documenting things
You'll be interacting with the iPhone the way Apple intended, which means you'll get the benefits directly from the source not through some filter.
I have found that the projects like Unity and MonoTouch are supposed to "save you time" but ultimately you'll need to learn their domain specific language anyway and will have to side-step things at times. All that is probably going to take you just as long as it would to learn the language you were trying to avoid learning (in calendar time). In the end you didn't save any time and you are tightly coupled to some product.
EDIT: I never meant to imply anything negative about .NET I happen to be a big fan of it. My point is that adding more layers of complexity just because you aren't yet comfortable with the quirky objc bracket notation doesn't really make much sense to me.
2019 update: It's 7 years later. I still feel the same way if not more so. Sure, 'domain specific language' may have been the wrong term to use, but I still believe it's much better to write directly for the platform you are working with and avoid compatibility layers and abstractions as much as possible. If you are worried about code reuse and re-work, generally speaking any functionality your cross platform app needs to perform can probably be accomplished with modern web technologies.

To add to what others have already said (well!): my feeling is that you're basically doubling the number of bugs you have to worry about, adding the ones in MonoTouch to the ones already in iPhone OS. Updating for new OS versions will be even more painful than normal. Yuck, all around.
The only compelling case I can see for MonoTouch is organizations that have lots and lots of C# programmers and C# code lying around that they must leverage on iPhone. (The sort of shop that won't even blink at $3500.)
But for anyone starting out from scratch, I really can't see it as worthwhile or wise.

Three words: Linq to SQL
Yes it is well worth the $.

Something I'd like to add, even though there's an accepted answer - who is to say that Apple won't just reject apps that have signs of being built with Mono Touch?

I would invest the time in Objective-C mainly because of all the help you can get from sites like this. One of the strength's of Objective-C is that you can use C and C++ code, and there is a lot of projects out there that are well tested.
Another thing is that you're code (language of choice) will be supported by apple. What it iOS 5.x for instance removes the support for a third party solution like MonoTouch? What will you tell your customers then?
Maybe its better to use a platform independent solution like HTML5 if you're not entire ready to move to Objective-C?

I've been using MonoTouch for a few months now, I ported my half finished app from ObjectiveC so I could support Android at some point in the future.
Here's my experience:
Bad bits:
Xamarin Studio. Indie developers such as myself are forced into using Xamarin Studio. It is getting better every week, the developers are very active on the forums identifying and fixing bugs, but it's still very slow, frequently hangs, has a lot of bugs and debugging is pretty slow also.
Build times. Building my large (linked) app to debug on a device can take a few minutes, this is compared to XCode which deploys almost immediately. Building for the simulator (non-linked) is a bit quicker.
MonoTouch issues. I've experienced memory leak issues caused by the event handling, and have had to put in some pretty ugly workarounds to prevent the leaks, such as attaching and detaching events when entering and leaving views. The Xamarin developers are actively looking into issues like this.
3rd party libraries. I've spent quite a time converting/binding ObjectiveC libraries to use in my app, although this is getting better with automated software such as Objective Sharpie.
Larger binaries. This doesn't really bother me but thought I'd mention it. IMO a couple of extra Mb is nothing these days.
Good bits:
Multi-platform. My friend is happily creating an Android version of my app from my core codebase, we're developing in parallel and are committing to a remote Git repository on Dropbox, it's going well.
.Net. Working in C# .Net is much nicer than Objective C IMO.
MonoTouch. Pretty much everything in iOS is mirrored in .Net and it's fairly straight forward to get things working.
Xamarin. You can see that these guys are really working to improve everything, making development smoother and easier.
I definitely recommend Xamarin for cross platform development, especially if you have the money to use the Business or Enterprise editions that work with Visual Studio.
If you're solely creating an iPhone app that will never be needed on another platform, and you're an Indie developer, I'd stick with XCode and Objective C for now.

As someone with experience with both C# as well as Objective-C, I'd say for most people Xamarin will be well worth the money.
C# is a really good designed language and the C# API's are good designed as well. Of course the Cocoa Touch API's (including UIKit) have great design as well, yet the language could be improved in several ways. When writing in C# you will likely be more productive compared to writing the same code in Objective-C. This is due to several reasons, but some reasons would be:
C# has type inference. Type inference makes writing code quicker, since you don't have to "know" the type on the left-hand side of an assignment. It also makes refactoring easier and more saver.
C# has generics, which will reduce errors compared to equivalent Objective-C code (though there are some work-arounds in Objective-C, in most situations developers will avoid them).
Recently Xamarin added support for Async / Await, which makes writing asynchronous code very easy.
You'll be able to reuse part of the code base on iOS, Android and Windows Phone.
MonoTouch largely implements the CocoaTouch API's in a very straightforward way. E.g.: if you've got experience with CocoaTouch, you'll know where to find classes for controls in MonoTouch (MonoTouch.UIKit contains classes for UIButton, UIView, UINavigationController, etc..., likewise MonoTouch.Foundation got classes for NSString, NSData, etc...).
Xamarin will give users a native experience, unlike solutions like PhoneGap or Titanium.
Now Objective-C has some advantages over C#, but in most situations writing apps in C# will generally result in less develop time and cleaner code and less work to port the same app to other platforms. One notable exception might be high-performance games that rely on OpenGL.

The cost of the MonoTouch library is entirely beside the point. The reason you shouldn't use Mono for your iPhone apps, is that it is a crutch. If you can't be bothered to learn the native tools, then I have no reason to believe that your product is worth downloading.
Edit: 4/14/2010 Applications written with MonoTouch aren't eligible for the iTunes Store. This is as it should be. Apple saw plenty of shallow ports on the Mac, using cross-platform toolkits like Qt, or Adobe's own partial re-implementation of the System 7 toolbox, and the long and short of it is they're just not good enough.

Is it worth porting a small C# "engine" to C++ or similar?

So, following a tutorial I found on MSDN I've created what you might call an "engine" using DirectX and C#. I haven't seen a lot of this sort of thing (Personally, that is) done in C# and the majority seem to favour C/C++ so I'm curious as to whether using C# will come back to bite me, or whether I should just go ahead?
The reason I ask is that the tutorial stopped rather suddenly and so there's a basis of something but it's small enough to be ported without much hassle. I like C# myself, but I don't know whether there's something everyone else knows that I don't.

Well Peter, the main reason is C++ is platform agnostic, while C# isn't in the true sense, despite Mono (I don't think you can run Mono C# on most cellphones, the Nintendo DS or the Playstation3, for example).
Anyways most of these engines support DirectX and OpenGL, and/or software renderers, thus they are engineered from the ground up to be agnostic. But as with any agnostic system, this requires a lot of effort, and resources.
Now from what you say, your engine is C# + DirectX, meaning your engine right now may run on PC, Xbox, Zune, and some Window's powered cell-phones. This isn't a bad range of platforms to be honest. So if your happy with this degree of freedom, and you prefer C# over C++ than you might as well stick with what you have, and spend the time improving your engine. However if you want to run your engine on anything not Microsoft, you'll need to make the jump to C/C++ sometime.
For an idea of what I'm talking about my team's engine supports Xbox,PS3,Wii,PSP,PC, and possibly other platforms as-well if we spend the effort, however we have 15 full-time engineers working on it, so... you see it's a big cost. Now if you want something like this for a free project, and you know C++ you may try any of the many open source engines out there such as Ogre or Irrlicht.

I suggest staying with what you are familiar with. Use of C or C++ should only be considered in your situation if you intend to do some lower level functionality, like implement your own image processing or create custom filters or transforms (depending on what you are using directx for).
Graphic applications can have computationally intensive aspects. Most of these have been addressed in the DirectX api- which is just as fast if you use it from C++ or from C#.
Where you would consider lower level language: If you are creating some image processing which could perform quicker natively- this only applies if it is not offered by the directx api, such as creating some custom encoders/decoders. In this case you could create the custom component in another language- and then load it in your C# application separately. If you are- look into using C++ Intrinsics, which allow you to program for your CPU, and also take a look at GPGPU API's like CUDA.

As a hobbyist game developer I greatly prefer C# (with a 3rd-party library call SlimDX) over C++. Yes, a game written in well-optimized C++ will probably run better than the same game written in well-optimized C#. But the time I save by using C# (I'm guessing very roughly 30-40%) can be used to optimize my algorithms such that a C# game will actually run faster than had I written it in C++ in the same amount of time.
As pointed out above, there's also the cross-platform compatibility issues because for most practical purposes a C# game will only run on Microsoft platforms.
Another issue to consider is that if you write your application in C# then it will require the .Net Framework to be installed on the computers it runs on. This can make distributing your application cleanly somewhat more of a hassle, though this is by no means an insurmountable obstacle.

There are a few studios using c# for games.
You can also have a look at XNA, there is also a port of quake3 engine flying around the internet ported to c#.
So it should be ok.

If you feel more comfortable in C# and there are no performance issues forcing to switch to a language closer to the CPU, then I see no need to change.
However, depending on what you plan to do in the future and how far this engine should be taken, that might change dramatically and C# might turn out to be the wrong choice. But this only time can tell, unfortunately. The right educated guess requires much more detail about the current implementation and about your future plans.