My cousin was the one with the top-end PCs back when Wolfenstein 3D and DOOM came out. Those games definitely rocked my world, never experienced anything like them. It's still a fun series to go back to.
It's interesting to read that Carmack wanted demons in the game so that no one could rightly be up in arms about blasting them away. Of course, that didn't prevent people from blaming the game for violence and supposedly teaching people how to have accurate aim with a real gun, but it always worked when my dad was concerned. "We're shooting demons, dad." (Worked in Turok 2 as well. "Sure, it's bloody, but we're just shooting monsters.")
id Software's crowning achievement is the first Quake, in my mind. Apparently it's most highly regarded for its multiplayer, but I've never played it that way; it was all single player for me, and that game had a great SP campaign. It was the epitome of old school shooter gameplay, far as I'm concerned. Did everything the old FPSs did but better and in full 3D with a spooky-ass atmosphere and enough new tricks and ideas to keep it fresh. To this day it's the most fun FPS to go back to, and it's one of the last examples of the arcade-style FPS genre.
That quote of Carmack's at the end about giving up on a game if it's taking too long—I'm glad that mindset wasn't in place during the development of Quake. They scrapped that game like two or three times with some remaining elements from previous builds, and from a much older Carmack interview I read, that's why the game has medieval enemies and themes amidst the technological occult environment. Worked out wonderfully, I think, giving it a very unique feel.