Jacob Christopher here, and I've got my review of Portal 2 - a short one. Portal 2 is an amazing sequel to Portal included in the Orange Box and is played a lot like Half Life 2 where your character is a mute and there are no cut scenes at least none that I remember. Portal 2 is essentially split into 3 parts. *SPOILER* The first takes place in the modern test chambers under the supervision of GlaDOS and Wheatley to link the story together. The second takes place in the old, abandoned test chambers build in the 1950s throughout the 1980s - I like this part as it switches art direction a little in the game and gives you an idea of Aperture Science's history. The third part is back in the modern day test chambers where you defeat Wheatley and you earn your freedom. The audio for this game is stellar, including the voice acting. This game pushes the limits of what the Source Engine has to offer. I haven't much to say about the Co-Op of the game yet, but from what I've seen browsing on the net, it is also quite spectacular - less story than Single Player, but more of a puzzle element.
TL;DR: This game is amazing, and you should get your hands on it ASAP.