I think there are some problems with monster generation. The monsters generated when the dungeon is created are not dependent of PC level, but those newly spawned while you are there are. I entered a new dungeon as lvl10 and killed goblins, rats and such. A few turns later I was being chased by troll brutes and hill orc chieftains.

Also, I'd say the rate new creatures spawn is a bit high, but that's a matter of opinion perhaps.

EDIT: Forgot to mention, newly spawned creatures sometimes spawn right next to you, I don't think they should do that.