Portal 2's co-op is strongest when neither of you know the answer: if your partner waits patiently for you, you feel like a moron if they don't, they'll be rushing you through all the discovery that makes the game great. The three-dimensional spatial thinking that makes the Portal series so addictive is only magnified when there's another friend getting stumped at the puzzles with you. As the two testing robots Atlas and P-Body, you and a friend get to explore the darker, more dangerous side of GlaDOS's testing routines-the stuff that's too dangerous for (non-protagonist) human testers. There's no denying the raw quality of Portal 2's distinct co-op campaign. Release Date: 2011 | Developer: Valve | Players: 2 | Steam
