What are some odd mapping quirks you love to see?

• As mentioned numerous times, voodoo doll scripting (three of the four maps I've had publicly released feature this quite prominently).
• TNT styled architecture that is both abstract yet appears somewhat functional at the same time.
• Excessive use of sector lighting effects (if you haven't incorporated at least thirty #8 sector effects in your map, what are you doing?)
• Plutionia-styled entrance/exit teleporters
• Map layouts that could by all means be nonlinear, but are in fact linear as hell
• Am I just describing my own mapping style?
• Environmental storytelling
• Small chapels full of pews that only serve to make combat more frustrating

When the whole (or significant part of) map geometry of previous level is contained in the following level. It could just be unreachable and serve as decoration. Then I'd love to find a way to it somehow and find something surprising, like an easter egg hidden in it, a la Duke3d.

Fake 3D in older ports: stuff like the suspended crate in Suspended in Dusk or the metal bar textures in Misri Halek always brings me a smile.

How did I not see this thread before.

• Loot closets. They spring open making you think it's a monster closet when you're low on ammo and health.
• Outside areas you can't get to.
• Torches in bases, tech lights in castles...
• Crushers that are made to look like moving parts in a machine.
• Flashing lights that are a clue to a nearby secret or is it just a flashing light.
• Crates that are bigger than any of the entries into the area.
• Secrets that have some puny reward like a single ammo clip.
• The old secret hidden in a secret.

Whenever some map manages to use the "pulsating light" sector special effectively. IIRC it doesn't really work as expected because it's constrained by nearby sectors' light levels?

Bit of a niche one, but sense of progression.

For example, level sets that go through a faux day-night cycle throughout the maps (I believe the Hell on Earth Starter Pack/Extermination Day does this in its Earth maps), seamless location transitions, and environmental change (e.g. a base progressively becoming more hellish and twisted as you get closer to, say, a portal.) It makes things feel more dynamic, even if it's just all set in place.

I also like the aforementioned environmental storytelling and levels that aren't centered around the player.

deliberate usage of ghost monsters

they're annoying to deal with but it forces you to think outside of the box since you can't just shoot them

The shoot-able switch and invisible bridge in Plutonia.

"The shoot-able switch" I really love those kind of switches, they really remind me of quake.