Portal 2 was the jump off, kid.
I'd actually put that as a runner up, maybe right under Dead Space 2. I hated the multiplayer in the game but ONLY because I tried playing it with 2 different people who had already beaten it with someone else, and instead of having a chance to figure out the puzzles they would either just do them because they already knew how they worked or would get overly frustrated when I couldn't figure it out
Also, Dead Space 2's multiplayer was ok, but forgettable. I kind of forgot that it even had multiplayer.