I generally feel like Quake's monster roster is fairly well-rounded (provided you're not picky about using them in an 'appropriate' level theme), but I really feel like it's always lacked Doom's "oh shit, I need to deal with this now" factor that you get from a well-placed Arch-vile or Pain Elemental.
Getting players to engage aggressively with encounters and not just endlessly backpedal away into safe territory is one of the big level design challenges of these games, and it does sort of sting to not have that tool at your disposal. Maybe this is why my maps tend to be so ambush-heavy.
