IF I ever had to put the lore of this expansions into a category of pros and cons, I would put it in both. It's been very all over the place.
The pros: The Jaina story arc was awesome. Some of the best storytelling Blizzard have done in years. Also the story lines involving the leveling were great too even though I hated the leveling this expansion the story telling in them was pretty good. I also enjoyed some of the Horde stuff.
The cons: The Sylvanas stuff has been questionable, her motives have been all over the place and the Night Elves, oh boy the Night Elves, getting 'their redemption' was just a cop out moment and another fucking slap in the face to Night Elf fans. Then again that isn't an issue that is exclusive to BfA, Night Elves haven't been treated well since Warcraft 3: The Frozen Throne.