It's Legion 0.5 !
Read the following sentences as if BFA came out before Legion.
War Campaign: A good feature that was poorly received due to rep gating and the super short and disengaging story.
SO it is expanded into an awesome campaign for each class with elements for each spec. The rep requirement is removed!
Heart of Azeroth: A good feature with poor implementation due to the slow progression that resets itself with each new piece. The catch-up mechanic isn't very good because AP isn't farmable at a good rate.
SO the progression now is based on Artifact weapons and is permanent and never lost, in addition to the AP being viably farmed from almost any activity in the game!
Missions Table: After the disaster that was the Garrison, BFA cuts back a whole lot on mission tables, making them virtually meaningless.
SO now they're expanded to have their own stories and rewards with a class-specific theme that's cross-faction. It doesn't isolate you AND it has some cool missions that can boost your gearing and income!
Azerite Gear: It was a bit wonky when you got a piece of gear that was 15 ilvl higher with the same exact traits but it was a downgrade because they were all locked traits.
SO now we have legendaries that provide an ilvl boost AND a fixed gameplay-changing trait!
Island Expeditions: They were boring and a chore.
SO we removed them.
World Quests: They were really good at the start of BFA, but as people finished their rep requirements, they became forgotten.
SO this time they'll reward meaningful things like resources for your missions table and a slight chance at a legendary!
Just a few thoughts on BFA. Not saying Legion was perfect.
From: Official WoW Reddit