Great game. Takes the formula of the amazing portal and adds on it greatly. Better campaign puzzles, and the introduction of user-made and co-op puzzles galore! It looks gorgeous too, the environments are teeming with character throughout and the way some puzzles reveal themselves to you - through a jittering wall or the falling of a glass panel or even the clean opening of a door - all speak to the various levels of the dilapidated Aperture labs.