nebulous

Great question!
It varies based on the game, but for a Half life example:
Understand your mechanics & keep your grip on the player loose.

For me as a level designer focused around combat, I want to throw players a problem, and I want to hear them throw a solution that's unique to them every time.

Don't mean to pry, sorry - but when you say combat do you mean like COD maps, or more PVE based maps with progression like HLA has?

for me personally, if I give players a problem, and I'm getting the same response back each time, then the problem I've given them is not interesting.

In the context of half life, always PVE.

interesting; do you prefer working on pve or pvp maps then?

you sound like a pve kinda guy idk what problems i face in call of duty other than shit aim

Originally I was really into PVP level design, although counter-strike disillusioned me to it since meta map choices and intense competitive focus in PVP games ballooned from it and made experimental concepts unpopular compared to simple & safe.