Are you being clever... or just annoying the hell out of the player?

Sometimes a map feature you're in love with turns out to annoy the player like crazy. Playtesting should reveal these of course but I think we can narrow down some things to be avoided where possible.

1. Lighting Issues

Flickering lights, torchlight and strobes should be used sparingly. Never use such lighting where the player has to make precise actions and try and avoid this in combat also. It can become very frustrating for the player.
I recently played through a mod where the extended usage of flickering lights actually made me stop playing. Round every corner was another flickering light, another esparking wire as the only light source. So frustrating. Use these lighting effects sparingly people and always have another low light source in the map so there is some light available.

2. Hideously precise jumping

Unless your designing an FPS remake of an 80s platformer (chukkie egg anyone?), keep your jumping puzzles simple and fun. Make sure each platform is obvious (no jumping on 1 inch wide pipes please) and if youre platforms are moving then playtest and tweak the hell out of it to ensure a good balance between fun and challenge.

3: Fake Doororama

Ever play a map where u spend youre whole time trying fake doors just to find the one that works? ANNOYING!
Fake doors are fine for detailing, just make sure the player understands visually which are fake and which are real. An easy way to do this is to only add door handles to the doors that work.

4. Repeating Noises

A looped sound effect can really drive the player insane. Sirens or alarms are usually the guilty party here. Make sure, if you set off an alarm you either turn it off again once youve made youre point or allow the player to turn it off themselves.
For background noise make sure you use the ambient noise set shipped with the game. Its ambient because it ISNT annoying on a loop...

5: Cluttered Play Areas

Theres nothing worse than attempting to run backwards with an enemy closing in and getting stuck on a random chair, or crate, or barrel that serves no purpose. Cursing the screen as you die once more... oooh the language...

Keep that detail to the edges people!
Keep the main playin areas clear and guide the players movements with railings, low walls etc... to ensure smooth, playable firefights...