Is this a quiz or something? The answer is Bioshock, I win.
I actually voted for Orange Box. I'm not a half-life 2 fan, never played the original or anything. Never played TF2. But Portal sucked me right in and was such an amazing and creative game. I have CoD4 and played the first few levels, but haven't gotten on multiplayer yet. But at this point in time, Portal wins. One of my new favorite games ever. Seriously I can't stop raving about it. Soooooo much better than boring, repetitive FPS games. And the challenge rooms are crazy, really make you think a lot (so long as you don't pussy out and use guides).