Ooh, are we tearing the OP's argument to shreads? can I join in?
Paper mario has the first claim to a 2.5 D platformer (well, maybe not first, but certainly before LBP)
Sonic 2 is only 2 player co-op but still good
The lost Vikings 1 and 2 are both 3 player co-op, and are some of the most incredible gaems ever