Saint's Row: The Third.
OK, this game was too fun. I would totally call this a must have for anyone looking for a non-serious romp in a goofy open world. The characters are all ridiculous and crazy, every mission involves massive amounts of destruction.
There is immaturity galore, from groin kicks, to a certain melee weapon to farts in jars. Some of the upgrades are hilarious. The story picks up a few years after number two, it seems, and right from the get go is completely over the top. Tank fights falling through the sky, the destruction of the city, zombies? all sorts of craziness.
A few glitches keep the game from being totally perfect but I easily overlooked them in the face of the sheer goofy fun i had playing. Only once or twice did i have a problem with getting over-run because of something goofing up in the game. It's a pretty solid, albeit completely immature, sandbox game.