I have to agree with The_Emperor, it is a shame that you don't have that many enemies at once any more. I used to love playing the original doom and having to kill loads of enemies (usually with a BFG :evilgrin:)
I'm quite used to facing imps now although its the revanents that r posing a real proplem for me. Also instead of wasting ammo to check if a zombie will get up whip out your flashlight and hit the corpses with it. It does the same job and you don't waste any ammo (pistol ammo is a rarity i've found and i'm constantly out of it)