These doors in maps:

[LeSwordfish]

You people are easily annoyed

The SPUF theme tune!

 

[Draco18s]

That would be funny... sick... but funny

I know, I know, I'm a Cruel Bastard.

Of course, I'd like to make a map like The Cube where things shift and move around (when no one's looking!) just to spice things up. "Ohshi-- this is different!"

Or a map where (most) of the (constructed) terrain is completely destroyable.

Or a map that takes place in "closed loop" curved space (eg. a space station that spins to create gravity: a strait line in one direction is a circle and you could shoot "up" at other people).

Or... *lightbulb, evil grin* ...I think I could do this...
A map that contains non-euclidean space in the XY position. That is, you could have 8 square rooms each adjacent to two others at 90 degree angles. You'd have to go around in a circle twice to get back to your starting location. It's buildable using cleverly hidden teleporters, one each in the doorways of 4 or more rooms.* Shame it's only doable in enclosed interior space ('nades, rockets, etc don't teleport, and large open areas allow for long sight lines causing other players to pop in and out of existence within view of another player).

*Depending on how clever you can be, both with the illusionary space and the entities involved.