BFA started with the Warbringers series, and after seeing Jaina's I knew that I wanted to play Alliance for this expansion. I love the Horde, but I tend to start as one faction, and change somewhere in between - pretty much SOP since Vanilla.
There were a lot of new systems to get oriented with, and of course the process of leveling up and raiding.Exploring the world was fun, Drustvar was an incredibly creepy zone. The other two in Kul Tiras were nice, but felt a bit generic. Not that there's anything inherently wrong with that - but just an observation.
Horde Zones I didn't get into until Nazjatar was released. They were cool tool - felt like they drew on Vanilla style themes, crazy desert place, wet jungle with dinos and dark jungle with spooky trolls.
The no raid sets was a much bigger motivation killer than I anticipated. Combine the fact that I had literally zero idea why the hell we're going into the asbestos factory (Uldir), I never felt much compulsion to raid outside of hanging out with friends.
The PvP mode was interesting, but seemed as more of an impediment than anything. I kept it off, unless I was specifically going to work towards PvP goals - which at this point was rare.
Additional zones that were added were, ok. They were too small to be their own expansion - but large enough to merit some regard when released. I did not like differences in the means of completion - WQs vs Dailies vs Spend Currency to solve this etc. There could have been a better, more rewarding balance here.
The stories of iconic figures (N'zoth and Azshara particularly) were wrapped up in one, two boss fights. Everything must end, but really, if we're not Gods at this point, what are we? Adventurers that have slain Gods, Titans, Demon Lords, etc - but still just adventurers?
Didn't like having to grind to be able to unlock the full functionality of my gear. I don't mind the AP system in and of it self, but requiring a non-trivial level of progress to use gear seemed punitive.
Didn't like being told for multiple expacs that "you don't need multiple armor sets anymore" and then having it switched to, "yeah, we want you to have multiple versions of these three pieces, also they're going to vary wildly in their effectiveness."
Legendary was a yawn, honestly, would've rather not had one.
Hopefully things are improved with Shadow Lands.