I picked up Portal 2 on sale this week and started in on the single player almost immediately. I have to say, while the game is good, it's just not the same as the Portal we all loved from The Orange Box. Things feel a bit too "on-rails" versus the first game. The jokes seem forced in some areas, and even though I'm not done with the single player, I just don't think I am going to be as satisfied as I was with the original game upon completion. Hopefully the co-op addition can make up for that, most people have suggested it does.