A small central arena (with a smaller central room) and a passageway (with secrets) around the outside. I think the intention was to make the central room only escapable by shooting switches, but the platforms that block access are player controllable... (Read that as: there's an easy way to get that spanker.)
A central arena (more action on the ledges than the floor, at least for us), and some outside narrow passageways. Author says powerups and rechargers were kept to a minimum... I guess we have different definitions of "minimum". (There are 2 2x rechargers, and a 3x powerup, that I found...) Teleporters in the outside corridors make sure it's never hard to find spanker-fodder...
A Waldo World-like arena, except that the ledges are much higher. Lighting favors snipers. Feels a bit claustrophobic, but that's not necessarily a bad thing...
There's a central room, but most of the action is gonna happen in the outside rooms and hallways. Watch the nasty corner rooms...
An interesting combination of area styles. Players (mostly) start out in small rooms, but there are teleporters and secret doors to bring everyone together... the main areas are long, open hallways. There are a couple of nice touches (the explodabob pit is always good for killing the guy in front of you, and the textures behind the rechargers are cool). Looks like 4 or so for optimal play...
Three enclosed rings. All the good stuff is on the top one, but you start at the bottom...
A simple arena, with pillboxes connected by secret passages around the outside. The only weapons are pistols, but it comes with a physics model that makes this fact irrelevant.