TMNT: Turtles in Time is, in my opinion, a definition of how to perfect a genre. It's so fun, so balanced and with so much personality. The game looks amazing for its era, the soundtrack is one of the best of the SNES games.
The game is a side-scrolling beat'em up, one of the best couch co-op games you can play. You can choose from all four Turtles, each one having their traditional weapons and fight style. The level design was really cool, making you travel through different eras of time. Plus having some really great boss battles.