Great game, as everyone else will say.
It's a great mixture of comedy and puzzling. The levels are well thought out and progress beautifully.
The only bad points I'll say is that i's very short, there never seems to be any sense of urgency and the very last thing in the single player is practically pointed out to you, so not very rewarding.
I can't really comment on the Co-op mode because of the PSN problems we're all having. So because of Sonys negligence Portal 2 has lost a star.
I was umming and ahhing about buying this or Gran Turismo 5.
I really wish I'd gone for Gran Turismo, as after 2 days I felt there was nothing left for Portal 2 to offer.