2 questions to start this posting off:
1) Have you ever played an adventure game? Probably, otherwise you wouldn't be here, and you know that they're (debatably) the most fun genre.
2) Have any of you folks ever played a Co-Operative (2 or more human players on the same team) game? Probably, then you know how much those can be too!
A Co-Operative Adventure game is something I've NEVER seen but (I think) would be more fun than any other type of game out there! If anyone's seen a game like this let me know, because I want to play it NOW :P
I've never seen any, but even if a few of these DO exist, I still think it'd be something EXCELLENT for Telltale to work on.
Maybe not in the game they're currently working on (with the caveman-looking guy up top?), since it's probably a good portion completed already and adding co-op would take a lot of extra work, but in one of their future titles for sure.