Perhaps the most interesting thing about Pain besides the monkey spanking, flopping bodies, fart jokes, etc. is that it seems to be a game that relies very much on building upon the game's foundation, be it from the player or SCEA. There is a finite set of rules, and the player then lets loose within the parameters in order to essentially create their own experience (to a degree).
And the developer plans to continually add content to the game. Pain will initially "ship" with a handful of multiplayer modes, allowing you to challenge up to four friends in how well you can cause, well, pain.