Something I can play with my girlfriend..
World of Goo made her want a Wii, she loves the puzzle aspect, the co-op play and the fact that the goo balls are cute and make cute noises :P plus she loves the art style.
I'm not saying copy World of Goo but..
I think you need to craft a game that has a good multiplayer aspect but can also be enjoyed alone, the characters should be entertaining - muttering one liners or having quirky animations for attacking or whatever they do..
Hope that helps.. :)







