That's something that I think that the devs don't quite get. It's all about intelligent novelty. Not really challenge or advancement, tho that matters some. But really the whole exploring thing, and the encountering of weird new stuff. That's the important thing. Repetition is poison.

The levels need to be better designed fortresses, not just random crap.

And there needs to be truly open-ended and smart generators for monsters.

Maybe a good quest generator too. That might be hard.