The dungeons have been vastly improved in Skyrim, Bthardzam was my favorite. It's a shame Blackreach wasn't utilized for more quests instead of going into the caves all the time. I would expect that the Winterhold college would be very interested in that place.
Dang, to be honest the dungeons started to blend together in Skyrim. Nord dungeons and Dwarven dungeons. Either a single area or a three tier area. Not much
But yes, Blackreach was very pretty (just learned that you can blast the ball to summon the dragon). Although Falmers were a piece of cake thanks to the fact that my sneak was out the wazoo.