I think some of the guild quests are super fun and the Vampire add-on Dawnguard is super cool.
But I can see way sou feel that way. The dungeons are often super repetative, pull chain, do that claw puzzle, do that whale, snake, eagle puzzle .get past the swinging blades, etc and especially the Dwemer Ruins are often overly long.
Also the thiefguild questline has one of the worst redundantly repetative quests I´ve ever seen in any game. That might have been the part I disliked about it the most by far.
I think the dungeons may be the weakest part. But try becoming a master thief for instance and it feels like you´re playing a wholly different game already.