Actually, that's one of the things that irk me a bit about roguelikes, even ADOM, who boasts a story and well-defined gameworld.
All the monsters are totally random... for example: I go into a gnome mine. I except to find ... GNOMES! They might keep some "pets", but it's absurd to find orcs, cats, blink dogs, worms, elves, lizardmen, and all sorts of things. Nethack is the worst in my opinion.
I like consistency. I'd prefer only goblins and every one of them to be semi-unique (character traits, physical traits & inventory), and that they'd develop strategies to kill the player - rather than meet an orc, a goblin, a bat and a giant rat (or somesuch) in a room. It just doesn't make any sense.
Heck, make some dungeon wars, where you find two factions in the middle of a struggle to take parts of the dungeon/cave you're exploring, that'd add even some more variety. Just don't add_new_monster_to_dungeon(random() % my_huge_monster_table_size>5000000)...
</rant>