From the master of cool tricks comes a bizarre, but thought-provoking idea... a mechanism by which you can determine the difficulty level at which someone is playing. The included demo simply has different terminal messages for each difficulty level (kindergarten through total carnage), but you could, in theory, use the technique to decide where to send a player, depending on what level he's playing on. The possibilities are pretty far-ranging...

A large football field, surrounded by seats (?). Nicely laid out, if a little bare... but ammo is really sparse, probably for anything more than two people. Gets a little better once you find the entrance to the control booth, but it's still not enough for bigger games.

A huge arena surrounded by rising hallways. With big groups, this might be fun, but smaller groups would have a hard time getting close enough to kill. There's a switch in the central pillar which I don't understand at all... all it seems to do is make the upper hallways vulnerable from below. Since only those in the upper hallways can flip the switch, it seems, well... pointless. (I suppose it also makes the area around the hill targetable from above... but there is much more freedom of movement down below, so it's more dangerous to those in the passageways.)

A square arena, with a ledge around the outside and a raised square fortress in the center. Simple, but well-designed for flow. The hill (The central fort) is accessible from both the ledge (via a bridge) and the bottom (via a fast elevator). There are a few pillars to use as cover... but more than two people in the game, and staying on the hill is a non-trivial excercise.