Help Me Find A Steam Game?

I have 20$ on steam and im looking for a game. Im choosing between Left 4 Dead 2 and Crysis Warhead but theres a specific type of game im looking for. I want a pretty colorful game like the graphics in Team Fortress and Battlefield 1943. It also has to be a pretty non-competitive game so co-op would be much appreciated. Preferably be a shooter or action game, not really looking at an rts or anything like that. Oh and above all i want it to be really fun and if possible i want the game to have good humor. Its probally hard to find a game that meets these specifics so just just suggest any good steam games for 20$ if you cant think of a game like this. The games i have on Steam already are: The Orange Box, Garrys mod and Monday Night Combat. Thanks