WoD was atrocious. The story was passable; they should have just gone all the way with the time travel stuff than this wishy washy nonsense. Pretending the expansion didn't happen was even worse than it happening. And this was all done to justify Gul'dan?
Well, we went from that... to Legion. Where Blizzard is finally introducing new story elements and building things up in a fairly interesting way, bringing everything full circle and having real character development on a large scale. Legion is, to say the least, impressive. But until I see where it ends I can't truly say if I like it.
As for the the other expansions and base game... in general, I feel like vanilla had an immersive universe (extremely so) but a very simple story -- if one at all. TBC had a pretty shallow story and made poor use of its assets. WotLK had very good storywriting for modern Blizzard; it may not have been highly compelling, but it was highly entertaining. Cataclysm was hot garbage. MoP involved a fairly compelling (and in my biased opinion, entertaining and immersive) story.
My opinion on WoW's lore in a nutshell, but Legion is promising and I look forward to seeing where Blizzard takes things next. Oddly, as soon as Metzen left the story got interesting... let's just call it a coincidence for now.