If you are more 2d guy
If it's your first game
If you have few technical skills
If your brain is like some dry potato
If you miss some precise ideas about the key points of the game
If you haven't a team and want to do this on your own
Do an MMORPG
Combine Braid with WoW. Instant hit.
Seriously though, if you're just starting out (sounds like you are), just make a Mario clone or something. Like Strider? Make a Strider clone. A small one. Maybe just one level. Or half a level. Don't worry about being original - why waste your originality on your first (shitty) games anyway? You need experience.
Do you have a 2D art portfolio? I'm a programmer/designer and I've got some small project ideas that could use an artist. See my portfolio so far: http://pupilgame.wordpress.com/other-games/