What's a relatively unknown game that has awesome multiplayer?

We all know about the kart racers, fighting games, Mario, Bomberman etc, so what's a great multiplayer game that you feel is under the radar? I pick general chaos as my number one with Herzog Zwei coming in a close second. It is a blast trying to put maneuver each other on the random generated maps. The humor is quite good in this game too, the comic included in the manual is always good for a smile. What about you? What's the under the radar multiplayer game that you and yours enjoy?