I would like to develop a game for windows 8, but since Xna isn't supported, i don't really know, if it is good to use something like MonoGame - because i think, it doesn't make any sense to use MonoDevelop with OpenGL while the UI Frontend runs with DirectX. But my searches and on "apptivate.ms", they still force the developers to use MonoDevelop - but why would a corporation like Microsoft even do this?
And i don't like to build my game in C++ with DirectX, because in my case, it's not a big game, and my favorite language (also, my language at work) is C#..
Btw., it would not be a big deal for me to write this game with OpenGL or C++, because I've got a lot of experience in these two for the past four years, but in this case, i like to have a "fast" and "save" solution like C# and a Graphics Framework.
So... maybe someone has the answer to these qustions:
Your question is ambiguous if you are referring to Windows 8 Metro (aka Modern) or Windows 8 Desktop, but I assume it's the Metro version.
If you want to develop a game in C# for Win8 Metro without using a commercial solution, you can use:
Concerning the previous answer, If Win8 Modern is assumed, you can't use OpenTK, as OpenGL is not a certified API for the Microsoft App Store and SlimDX is not compatible with Windows 8 Metro.