Innovative FPS Features

Having played all differnt FPS games from Halo to Half-Life, ive seen some very unique feature that set each game apart from each other and are polished so well that it is the first thing that comes to mind when you play. Now me, as an indie, love playing these games but wouldnt want to make another one that people will say "this reminds me of so and so", or "they took that from this other game". I want to make a FPS that people will say "nice Ive never seen this before." Now my game is coming along just fine but i still have no concrete "Innovative" features or something to set this apart from the other games. I did have in mind a cause and effect type of gameplay but i want to start small so it wont take me 7+ months to finish this game.lol

So i have come to all my fellow torquers to ask:

What do you want in a FPS that you have never seen before?