Classic (I know it is not an expansion)
BC
Wrath
Cata
MoP
WoD
Legion
Cataclysm. I wanted to like the new changes to resilience, but all they really accomplished was slow small-scale PvP down to a crawl. Then there was also the matter of the talent trees being messed with and, as much as the changes were well-executed, any savvy observer could tell that it was the beginning of the end of character progression as we knew it.
Raid design also took a serious hit beyond the first tier, even though the dungeons themselves were a high point of the expansion.
Personally i have to say WoD/Cata. WoD ended up being a paid facebook game if you did not raid at all (bar lfr or something) and Cata was just awkward imo. Did like MoP, but tbh WotLK still reigns supreme for me.
The only good thing WoD had was the best intro cinematic till this day but thats it.
legion class design can't compare to mop. imo MOP was the pinnacle of class mechanics
Cata by a big margin.
People think that WoD had bad story, Cata had no story whatsoever. Ozumat kidnapping Neptulon had no conclusion, Uldum ended up as big Indiana Jones joke with random war on the background with Al'Akir elementals and titan lore being mostly ignored. Deathwing didn't have any story besides little questline in Twilight Highlands. That's on top of having least amount of raid bosses in all expansions (most of which were shit too) and shitton of content cut out.
Legion for sure. While WoD and MoP had their downsides as well, the RNG and grind going into Legion is just unreal. Roll-your-luck legendaries and gear entire tier levels apart based on randomness is not something I appreciate in this game. If I wanted Diablo, I'd play Diablo. Well, I am playing Diablo, but that's beside the point.
I'm going to pretend like I didn't read the insult but what exactly is your point? The lore of MoP was horrible. Maybe if this was a kid's game then it might have fit in. But pandas... really? What's next, an expansion based around unicorns ?
The bottom line is the Pandas really took a lot away from the warcraft "lore". I get they were trying to make the game more appealing for their Asian customers but it really killed a lot of Americans/Europeans from actually enjoying the lore. Nowadays, people don't even care about wracraft lore anymore and that has driven a lot of people off.
WoD... Cata was bad, but forgivable. Legion is looking like diet WoD with less bad, but could still go either way