The problem isn't planning to make a game or even the storyline or genre you choose, the actual problem is finishing the game.
Most people around here start creating a game, but never finish it. There only have been few who were able to start a game and finish it. Imo a 2-3 level game isn't a finished game at all, that's a demo.
The problem is staying focussed. I can tell you about 10 ideas I've got for games, but I did not even considering them seriously until I finish my current game. Which I've just done (follow my signiture link if interested), so now I've been considering possible ideas for my next game. By now I've made my choice and it's quite interesting what I've choosen as my next project. But I'm not going to reveal it until it's done.
FPSC will not create doom 3 of half-life 6 or even quake 99, but you still can create a good looking, fun to play, more then 1 level game with it.
