core gameplay should be fun, story, art-style etc.. are all after the fact. If it isn't fun with stick-figures then it won't be fun with photo-realstic characters, a dramatic plot and epic music.
Find a buddy or two and whip up a prototype, nothing big, a level or even a piece of a level, that can show the gameplay/overall experience in a compact package. Like Justin said, if it isn't fun with stick figures it isn't going to be fun in full next-gen or stylized or whichever art direction you choose. Starting small…
What everyone has said here is pretty nice and accurate and said a lot less nastily than I would have written it, if I had seen this thread earlier. I, too, have hundreds of pages of "design" docs for a game I wanted to build. The problem I had with not knowing anything about art or programming is that they're not the sort…