When it comes to game development, my favorite wish would be that XNA was made available on WM, and a secondary option might be a WM version of 3DUnity (that now supports iPhone). But since there are no immediate plans for either, I have spent some time checking out the game engine market (especially for WM and CF development), and found the following...

...and a typical game server is provided by Exit Games but there are several other options. For someone who wants to cook their own game server, I recommend to check out the old (but still very valuable) AUTD article by former MVP Alex Yakhnin.

My personal take at the moment is that since we already see OpenGL ES in some important WM devices (HTC Diamond, HTC Touch Pro, Samsung Omnia, etc), that might well be the way forward when it comes to 3D game development on most mobile devices (not only WM, but also iPhone, Symbian, Android, etc). It seems like DirectX/Direct3D is actually just a wrapper for OpenGL ES on the devices that support it, and some rumours also indicate that OpenGL ES will be a core requirement in WM7 devices. So, my bet going forward is OpenGL ES and the wrapper by Koushi above is a good starting point (some samples are Sensory Overload, GL Maps, and Diamond Beer). Also, a great source for learning OpenGL (ES) is NeHe.

That said, the current state for building simple games for most existing WM (5.0 and above) devices is GDI, and even if somewhat limiting when it comes to capability (2D) and performance, it can still be used for simple games (board, slow-moving, etc).

Any cool game engines that I missed?