Rayman Origins is the definitive cooperative platformer. Best couch co-op of the entire generation as far as I'm concerned.
I'm going to assume you haven't played very many "couch" co-op games this generation.
Portal 2 is the only other thing I can think of that even gave it a run for its money. The frantic fun of doing some of the harder levels or Tricky Treasures or what-have-you with three friends is an experience I won't forget any time soon. What game(s) do you believe surpassed it?