Alliance was three zones all with the same concept: one of our allies betrayed us.
Then the Drust were entirely undersold. They never get established as a major threat, only a localized one, and we clean them up by zones end, it was just awful. You are left wanting more and with their leader dead and their followers demolished, we'll not be getting more. What was the point of all that cool wicker stuff?
Nor does it help that Stormsong and Tiragarde are both zones with very small storylines and then lots of disconnected filler. You go in and you're done with the major plot point in an hour or two.
I've heard many say that Alliance has more world building. Which is somewhat true. Except that world building largely happens in the major plot lines anyway, the filler just remains pointless filler.
Then of course Kul Tiras is just all humans all the time, which makes the zones merge together all the more. Again I've seen the argument "Well its Kul Tiras of course its all humans!". But then on Horde side we have major storylines involving Vulpera, Sethrek, and Tortollans. Alliance doesn't have anything like that, just constant human. All with a nautical theme; at least the evil trolls look entirely separate from the others.
I keep seeing the same thing in defense of the Alliance story: its building towards something. And I dont see it. Azshara is only a "major" player in one zone. Outside of that Alliance has kul tiras now which is now united under Jaina; unlike Horde who, yes, do have the Zandalari, the empire itself is shakey due to the wildcard that is Bwonsamdi. Likewise when we get more Azshara stuff you can guarantee Horde is also going to be involved in their own way as well so it wont be an Alliance only thing. Alliance isnt building up any more than Horde, which arguably has more on its plate with Sylvaanas, Saurfang, Bwonsamdi, and Vol'Jin
EDIT:
This is all ignoring that the Alliance zones are also far less varied. Horde has a normal sort of open air zone with lots of temples. A dark evil swamp. And a desert.
Alliance has: Verdant valley. Hilly valley with darker skybox. Mountainous valley with an even darker skybox.