Transformers: War for Cybertron.
Already finished Campaign, which is short. Now playing it for the Multiplayer, which, to me, is Amazing.
There's just something about going invisible, turning into a car, sweeping in, backstabbing the hell out of someone's ass, changing back to car, and running the hell away that is just soo...awesome. Not to mention the other classes with their own playstyles and vehicles...and it's rather well balanced, too, for a Class-based multiplayer game.
Oh, and of course the familiar Transforming sound makes me Nostalgia/Nerd-Gasm everytime I hear it...