I wrote an xbox game over the weekend; finally got around to posting a movie of it today. You can download the movie here. (I recommend viewing it w/ VLC).
The game is a t3tris clone, but it does a lot more than your average clone. The blocks themselves are actually stored in their own independent data structure rather than a giant array like your typical t3tris clone. Storing the blocks in this manner allowed me to do per-piece bump mapping and some nifty little physical simulation-esque effects. I also added a particle system effect so that when lines are broken they appear to blow out of the stack. Currently the game is only one player, but it should be easy for me to make it four player... my goal is to get Tetris Worlds (R)-equivalent functionality so I can start experimenting with multiplayer t3tris game variant ideas I have. I think adaptations of t3tris that include "screw your neighbor" elements like Swordfighting in Puzzle Pirates are great party-game fun, but nothing like this exists on Xbox.
Xbox development is actually really easy. Xbox is basically DirectX 8.1 w/ some extensions to make common game tasks easier, like controller input, saving state, etc. Xbox also includes a whole slew of debugging tools for performance profiling and shader debugging. In some ways its even easier than PC game development. I think if I were to write a PC video game I would actually start on Xbox and then port it back to PC. :-)