I'm not much of a DoomRL player (yet), but I'd recommend Tough as Nails and Ironman (in that order) over Brute. Additionally, sneak around in Coward, and switch tactics when in melee range. Make sure you're always wearing armour, carry lots of medkits, find a chainsaw as soon as possible, carry some clips of ammo as bait, and of course step by the UC if you're up for it. What also helps is to keep your field of view limited by avoiding wide open spaces.