One of the best puzzle games to date...with co-op! It's amazing how having a friend along for the ride can make the Portal experience that much more fun. The same charm and wit from the first game return, refined to an even higher degree.

More puzzles to solve and Steam Workshop integration means you can play Portal 2 for an incredibly long time, not to mention P-body, ATLAS, and GLaDOS's hilarious interactions. Give this game a shot with a friend and prepare for an unforgettable experience.

100%: Unsurprisingly, there are numerous co-op achievements that you will need a partner to help complete.