God bless modders; they don't settle for less. When Just Cause 2 was released, it was praised for its huge expansive world and chaotic, sandbox fun. But modders asked the question "Wouldn't this be even better with like.... about a couple hundred people playing multiplayer?" And by the looks of the trailer above... yes. Yes it would.
The new Multiplayer Mode DLC for Just Cause 2 looks like the ultimate "dicking around in co-op game" of all time. There's races on land, sea, and air; massive shootouts; and just the sheer craziness that's going to happen when there's a huge amount of people in a single virtual world with no rules. Of course, I've heard reports of some bad server lag and the game being unable to cope with such a large amount of player characters inside it but this seems to be a mod where players will make their own fun.