The co-op in Portal 2 was an enjoyable experience when I played it with a close friend. It was fun trying to figure out how to solve each puzzle and none of the puzzles felt overly difficult to solve. There was additional fun and challenge added in when trying to earn Steam achievements/PS3 trophies and find...
Main co-op campaign is short
Creates a sense of accomplishment through a high level of teamwork
Co-op does not punish when you want to goof off with or troll the other player
Challenging puzzles that require creative thinking