Portal 2 will keep you up for days.
Juste beat Portal 2, total mind-f. The ending is crazier, the writing is perfect, the puzzles go beyond test chambers, and it's perfect. It's better than the first one, and that one was one of my favorite games of all time. I'm going to play through again tonight with developer commentary.
Has anyone tried the co-op yet? The single player story arch is some of the best I've ever played. Can't wait to see what new experiences co-op brings to the table.
Also, be prepared to play multiple levels with no commentary. It is much more spread out than in the first game.