Portal 2 is available at 50% off now through Thursday at 4pm Pacific Time.

Also, FREE DLC just released! Peer Review is the first DLC for Portal 2, the year's most brain-bending action-adventure game. Featuring a devious new co-op track that continues the story of Atlas, P-Body and GLaDOS, the DLC also includes both single and multiplayer challenge modes, plus leaderboards so you can compare your portal placement and time scores with the Portal community.