Haven't really thought about that before, but I'd most likely do some sort of fantasy RPG game.
For Xbox360 and/or PS3 preferably, as I don't really like getting new PC games, because I must have a computer with rather good engine (which I do not have atm) to fully enjoy, but with console, I don't have to worry about that so much, it'll run fine if it's made to run on it.
As for the game genre, I chose fantasy RPG, because you have so many things you can choose from, almost anything when you're making a game of that sort! =P