Well it's supposed to simulate the old abandoned dungeons of the keep, replete with secret passages to sewers/catacombs abandoned long ago, it's just not complex enough to really make it look like this yet.
Based on the one I've taken the time to extensively explore (and clean out) they can be fairly complex. A lot of stairwells, 10 levels, passages that don't necessarily meet up. In my current dungeon I found a whole second wing after clearing out what I thought was the main dungeon of humans (probably close to 20 of them.) The second wing had dwarves (which eventually spammed me with crossbow bolts), and I think I barely scratched the surface of it.
When I was clearing the first floor, I thought initially that bad guys were respawning somehow, because the same group of lashers and pikemen would meet me in the same spot every time, even after I killed "the commander." In reality what was happening I think was all the human baddies in the dungeon slowly filtered up toward that spot over my repeat visits, until I finally killed them all. That was probably close to 2 hours of non-stop dungeon crawling until the dwarves brought me down.
So yeah, I think the dungeons are
plenty complex (if a little redundant.) The stuff in them just needs to be found a little deeper, or be spaced out a little better for game play purposes. Entering the first room and running into 7 guys is just kind of a kick in the balls, since everyone is recommending going straight to the dungeon to get gear. Personally, I found it way easier to kill half a dozen werebeasts and get some skill up first.