Things are beginning to look up for me being able to do some XNA-based projects in the new year. I need a couple realizable games to tackle. I have one designed that I'll never be able to get approved (it's called "Fanaticize me!" I think I'd get in trouble even by describing the playing pieces).
I'm thinking it would be a better idea to do a physics-based simulation a la Line Rider. I'd never heard of that particular one until today. It looks like a lot of fun (of course, for me, it's more fun to program it than to actually play it).