I liked it in Travail when you walked to open a door and got the subtle message "Kill Cthton first".
As the Cthton was rising up behind you.
As you mentioned, True Love Waits is the defining moment of terror for me in Quake custom maps... Zerstorer in general is the absolute best of the best, atmosphere-wise.
Other moments that spring to mind are the shambler ambush at the start of Tale of Abbot's Rune and the absolute evil of, well, The Middle Evil.
posts for this about five times now and every time I get interrupted..
didn't czg make a map that played the shambler sight sound on a random trigger somewhere?
I Remember A Q2 Map
that played the Gladiator sound right at the start, as soon as you first stepped in...
Which, if I recall correctly, spooked Daz so hard that he fell into the lava.
these remind me of negke's map (lower forecourt) which starts with two shamblers right in front of you in full-on smash/attack animation - but it turns out they're statues. That was awesome. some of the traps / setups in that map were really difficult to deal with.
I remember one map way back when, where you'd kill one enforcer, and it would teleport another in one right behind you - it did this like 6 times, hahaha!
Two That Come To Mind
mexx series for mid boss and gameplay setups.
Kona maps for unworldly architecture (even though his stairs are a pain in the arse to navigate...)
that nobody has mentioned ijed yet. To me he is the master of infusing a pervasive sense of dread into every corner of a quake map/pack.