I've finally finished my second XNA game:
Sumo.

"A frantic multiplayer shooter / brawler you can play with your friends or AI Bots" according to my news item :)
It's available for Windows and Xbox.
Bots aren't brilliant but at least they provide some fun for when your mates go AWOL.
Total development time was about 6 months - part time, probably 1 or 2 hours per day.
Have fun - feature wise it's complete because I'm itching to move on to something else but shout out any bugs you find and I'll bundle 'em up into a patch release sometime soon.