Generally, when I get ideas for games, I disregard them if they can be summed up in less than 5 or so sentences.
If you want to make some truly original games (which is what the industry needs right now) then your game shouldn't be able to be described as follows:
Like (existing game) but instead of (blah blah blah).
Adding more players to an existing title is not effective game design :/
Don't worry though, great ideas will come; They always do.
PS - I try not to fall into the trap of "It doesn't matter if it's been done before if you do it better." This is what the FPS market seems to be doing. They just make the same game over and over in an attempt to make the best ultra-realistic, light-bloom filled, repetetive tactical shooter. And it's working.
