I consider Skyrim to be a masterpiece, but the one change I would make is reverting spellcasting to work like it did in oblivion.
There's a lot of writing issue in that game, in game writing in case you were about to say "muh lore", single quests and questlines also suffer from how bland most of them feels when compared to past games and guild quests being one worse than the previous one: the companions is ass, both because it forces you to become a werewolf, which isn't a mechanic that was particularly developed and i'd argue it's not that great even after the dlc, bethesda's overelies on radial quests for this guild and the rival faction of the silver hand is literally just bandits with a fancy looking sword that can be looted from their corpses; mages guild are arguably worse than in Oblivion, dark brotherhood's offers you sidejobs that are on par with the infinite radial quest slob that you're forced to do to become master of the thieves guild, which also has about 2 good quests and forces you to give away the skeleton key and soul to nocturnal.
Enemy variety isn't so great either, the best example is to compare any random undead dungeon between oblivion and skyrim: In oblivion you meet mainly skeletons wielding random large weapons and able to summon weaker skeletons, alongside zombies that are much weaker but carries diseases, ghosts/wraith that cast spells and/or uses 1 handed weapons and on high level liches that uses a staff and magic; skyrim has daugrs. daugurs comes with either the ancient north or for champions, extremely ugly looking ebony weapons, daugrs aren't fun to fight, but you're gonna fights dozen of them because of what feels and probably is like 90% of skyrim quests. Magic in skyrim is dogshit, with dragon shouth being fancier but requiring killing the same boring boss multiple times and, speaking of which dragons aren't good to fight, they're argually worse than closing oblivion gates due to their shitty moveset that makes the guardian dragon from ds2 look good in comparison and 3 are required to fully unlock a shout.
Skyrim's paradoxically suffers a lack of content and overabundance at the same times, there are lot of missions and dungeons but mostly feel the same since there's not that many enemies to fill them; quests are virtually infinite and at the same time there aren't enough good quests, fancy spells and type of spells, but a lackluster amount of spell effects and there's only one way to unlock dragon shouths that isn't really that pleasant.