It certainly added a lot of tension to the games - as you're reaching the end of the level, your health is looking low and a phase 1 Dark Trooper pops out:
I really did poop myself the 1st time that happened. The atmosphere of the game really sucked you in. DF2: Jedi Knight was the last in the series that made you feel like you were in that world.
Doom is more of a shooting gallery than an in depth proper adventure. I still say that Doom's shotgun is the best weapon in any game ever!