Portal 2 remains one of the funniest and most inventive puzzlers in games. It successfully built on the mind-bending multidimensional ideas of the first game and somehow elevated its storytelling and characterization to become incredibly fun and memorable. Those things alone would make Portal 2 worthy of your attention, but there's additional content that comes with playing the game on PC. Not only is there online and local co-op that extend the game beyond its single-player offering, but there's a huge amount of user-created content that includes whole story campaigns.