Still working on Doom 3, and besides the ever-present flashlight thing, there are a few other elements that I'd personally qualify as poor game design, or at the very least as annoying. I think Id was trying to go for a straight-up survival horror feel, but they translated that to having new waves of enemies spawn almost every time you walk into a new room, or grab a conspicuous health pack or ammo dump, or have to backtrack to a previous area. The scare effect doesn't work when you know it's coming around every corner, and I just wind up mashing quick-save every minute in case the next one spawns right in my face and shreds most of my health. On top of that, while the demons randomly spawning in via portals make a decent amount of in-universe sense, what doesn't are the human zombies hanging around behind all sorts of panels that seem designed solely as hiding places for them. Nothing kills immersion faster than really game-y elements like that.
Also, like 98% of the game has taken place in the same exact future-industrial-tech environment. I mean it's a cool look, but dear lord, I want to be able to stare at something other than a bunch of pipes and gauges.