Sequel to the acclaimed Portal (2007), Portal 2 pits the protagonist of the original game, Chell, and her new robot friend, Wheatley, against more puzzles conceived by GLaDOS, an A.I. with the sole purpose of testing the Portal Gun's mechanics and taking revenge on Chell for the events of Portal. As a result of several interactions and revelations, Chell once again pushes to escape Aperture Science Labs.
Verdict
<1week
You'll breeze through this one.
Expect a serious time investment past the main story.
Portal 2: Peer Review includes an additional course for Portal 2 co-op campaign, dubbed "Art Therapy"; as well as Challenge Mode for both single-player or multiplayer campaign, where players can play specific levels and compete in friends/worldwide leader-board.