Doom of course. Whenever I hear any piece of media use a sound effect from the game, I immediately think Doom. Yes, even Doom used a lot of sounds from a sound bank back then, but it is what made these sounds instantly recognizable everywhere.
Blood. Spot on soundtrack (MIDI) and I especially like the explosions, Gargoyle growls and the cultists in general.
Serious Sam. The sound plays an extremely important role as it allows you to tell in advance what's heading your way and to also dodge enemy attacks without having visual contact with all the enemies. The rumbling of a Sirian Werebull rushing your way is a good reason to panic :P
Shadow Warrior 2. The combat is so visceral and meaty in large part due to the sound. Especially enemy screams/suffering are spot on when you set them on fire or electrify them or just straight up splatter them with a huge critical hit. Makes me look forward to every next group of enemies to ruthlessly dispatch. Also, the main theme songs both in Shadow Warrior 1 and 2 are incredible.
Unreal 1. The soundtrack along with the ambience and level design creates an incredible feeling of wonder. It must have been completely mind blowing, playing it back then right when it released. I missed it by a couple years and was still amazed. Especially the translator message sound really stuck with me.
As you can see, it's mostly FPS games for me, as the sound design there is very important/noticeable.
Edit: I can't remember if I brought this up already. Apologies if I did.