Kameo supports co-op. . . but it's not really "story mode" co-op. You can only play co-op levels once you've unlocked them by beating them in single-player mode. I haven't tried it out yet, but I hear it's not all that great.
I would love a game like X-Men Legends, Baldur's Gate: Dark Alliance, or even Tales of Symphonia, that was designed from the start for multiplayer all the way through. Those were some of the best, most addictive gaming marathons I've ever had.