Play the first Portal entry before you play this one! You won't appreciate the first game if you don't as it's still a true classic.

Portal 2 takes everything that makes the original title so amazing, and expands. This game is everything in the first game, but more, and with loads of bells and whistles to make it a brand new installment, and leaves just as big an impact; which is remarkable considering that Portal broke many boundaries itself. Innovation is a good way of describing this game.
With more, cleverly designed puzzles, a greater story, and even more memorable characters, this is an absolute must for any Steam owner.
A virtually flawless game with tonnes of content besides the main story, with a Co-op, a test chamber workshop, you'll have plenty of hours of fun with this one! Valve truely outdid themselves with this title. Buy it now!