You basically have three options when wanting to create video games:
  • Create a Silverlight Game.
  • Create a C++/DirectX Game.
  • Create an XNA game and port it to Win8 via MonoGame.

Create a Silverlight Game
The idea is simple. Just use the default XAML controls to create an awesome game!
Silverlight: Learn: Silverlight.NET

Create a C++/DirectX Game
This is what Microsoft recommends. You have to do no extra work and simply use VS2012 to make an awesome Metro Game.
Tutorial: Shape'12: How to create your first Windows 8 Metro-Style game | Channel 9

Create an XNA Game
This is a little more trickier. You need to port it using MonoGame. You can also port your XNA game to Mac, Linux, iOS, Android, and more for free!
MonoGame: MonoGame - Write Once, Play Everywhere
XNA Tutorial: XNA Tutorials - RB Whitaker's Wiki

An Example of an XNA Game [My Game]: