The worst expansion:
Story - Sylvanas masturbation; every plot line was a massive let down: Tyrande and her revenge, Jaina's "Beware of me LUL", Bwonsamdi involvement didnt mean anything beyond two raids. Saurfang got his death though, Baine got his place in Stormind. There is no promised faction WAR.
Features - massive niche stuff and mostly failure: Warfronts - failure, Expeditions - Failure and niche entertainment; Azerite Armor/HoA/Essences/Corruption gear are pile of shit on top of pile of shit. This should have been introduced on 8.0 and not on 8.2.
PVE - just average. Like, why the hell do you make LFR mechanics in every raid harder than Normal or even Heroic? Dungeons are mostly mediocre and designed way worse than Legion dungeons. The WQ and quest chains are mostly boring and tedious and sometime feels like full time job.
PVP - ??? its just there. WarMode failed spectacularly.
Classes mostly are oversimplified and revolve around two-buttons mechanics. Also GCD. Its huge letdown after Legion.
3/10 add-on. It has nice starting experience in terms of leveling, but thats pretty much it. Classes flaws ultimately couldnt compensate the bad content so yeah, it was very mediocre gameplay experience all around.
And guess what - it could have been passable if there was alt-friendliness. There was big middle finger instead.