[*]The Daedric quests are always a waste of time because the rewards are crap. The exception being Azura's Star.
[*]Every recurring series quest line (Thieves Guild, DB, Mages, etc.) was worse in Skyrim than in previous TES games (except for the Thieves Guild).
[*]The Blades are useless and lame.
[*]Magic is breathtakingly useless. All mage-only characters should be deleted in protest.
Not having custom spells is a travesty above all others.[*]
You should be able to kill any NPC you want (even essentials) and fuck up your game beyond all reason.[/list]