I just submitted my first game to the Windows 8 store for approval. I call it joyrider.
In this game, the player is given a small ship and is put up against 12 levels of other ships; sometimes fighting 10-20 enemy ships at a time. The game objectives unfolded as I experimented with asteroid-like space physics and a flexible ship/weapon system that could be used in a future RPG-esqe game. This game is a simple arcade shoot em up though, it certainly is not a 'digital world' game.
Joyrider is written in C# using the MonoGame module. I am finding it to be very enjoyable programming in C#, once I passed some original hurdles. It now comes as naturally to me as Actionscript3.
Joyrider is a return to my multiplayer space shooter, Star Sky, but with a very key component missing... The multiplayer. I am using Joyrider to learn C#, but it has turned out really good, so I went ahead and submitted it for publishing to the Windows store.