It seems like a kind of punctuated difficulty. There's long stretches where you're basically just walking through the bad guys, no trouble, then there'll be a fight where you have to pull out all the stops to survive, then another stretch of nothing.
I had a fight where, after going through most of the second floor without going below 40 HP, all of a sudden I found myself getting thrashed by a freakin' Enraged Diggle group-leader with a nasty set of fire-based buffs. I was actually running around with 1 HP for a could turns, and killing him was a good gamble less than a strategy.
Luckily, I didn't make the same mistake when I finally opened a Zoo. Took two teleporting potions, a half-dozen Ampule bolts, my entire supply of Dire Sandwiches and regen-mushrooms, quite a few traps, and exactly two Bolts of Mass Destruction. Close, really close.
Now I'm regularly finding myself in iffy fights on Floor 3, because Octos are bastards. I'm not in a tremendous amount of danger, it's just every fight feels like the game is deliberately trying to gank me. Oh well, I have the best craftable suit of armor in the game (Embossed Serpentine Platemail), the Vampire Hunter's Hat, a kilt
and champion's belt, a Doubleplus Crossbow, and a Cybertronic amulet. 43 Block Chance, 19 Armor Absorption, a crapload of resistances, and 21 Melee Damage. I'm running out of trump cards, but I'm still a god for now.