As for the gameplay, slightly different from the first game but it's still left button fires blue portal, right button fires red (or orange for people who aren't colorblind).
The game is much longer now, it goes on for at least eight hours (about nine for me, I spent a lot of time having fun with the various gels).
The story is brilliant, I won't reveal to much since that would spoil the surprise for anyone who has not yet played the game (which I recommend they should do by the way). As to be expected, there is a lot of humor in the game, they got some fantastic voice actors to do the different voices that guide you through the levels.
I have already posted a review on ModDB, I gave it a 10/10 naturally. And to anyone who reads this post (and has not yet played Portal2) I once again say, play it and you wont regret it.