I don't know... The dungeons are varied, to an extent, but they're still largely the same. Earlier today I walked up to a fort that was little more than a tower on a hillside. Before I even entered, I knew what palette was going to be used for the place and I knew I would be fighting bandits/Forsworn (I was in the Reach) or mages. Why? Because that's the way it is with pretty much every fort.
I wasn't disappointed, either. So then I did what I do with every fort or old ruin I come across. I went in and I killed everything. This particular time it was magic spiders with a mage at the end.
Yes, it starts to feel repetitive. You find a dungeon, go inside, face the same sets of enemies and kill them all. Go to the next and repeat. Sure, they try to work stories into them, but usually fail pretty badly.
What do you expect a cave or a ford to look like then? What other enemies do you expect? Which other games (with modern assets) do you play that offer more variety in both enemies and world building sets that doesn't charge a monthly fee? Of course assets get reused, every game does that. And the longer and bigger the game, is the more assets get reused.
But I think they did a good job at telling all these little stories in dungeons, and mixing and matching building sets for a slightly different look each time.

I haven't gotten bored, I haven't thought once "This is getting repetitive", instead I've been eager to explore the dungeons. But maybe that's just me.