i think a good dungeon design isnt necessarilly about having tons of enemies, but an overall interesting group of encounters(not just bosses), a few multiple paths, with slight randomization. and perhaps a few special things. I havent played it recently, but before blade and soul had fairly good dungeon design. It was pretty varied, most trash fights had appropriately interesting mechanics. like sometimes you needed to kill specific enemies, some time lazers would spawn in rooms, or you had certain traps. Some times you had to burn an enemy, survive an onslaught, run away, some you can smartly avoid. sometimes randomized thing might make you take a different path or fight a different challenge, and they even had a few hidden events with rare loot here and there.

Also weapons were usually upgraded from various loot, so everyone had reason to do them multiple times.