Looking back i think a big lasting appeal for Heavensward was being a modern MMO expansion where its not an 'everything your know and love will die because this time it really is the biggest bad ever, swear on me mum' that causes so many other MMO's to fall apart narratively as they succumb to antagonist fatigue. In HW you are on the lamb and get caught up in what is essentially a blood fued. A few families killed someones sister and he refuses to let that go even long after the perpetrators are dead. Its just a war that in no way is effecting eorza proper and its doubtful Nidhogg could have done a fraction of the damage Bahamut did so its less "heres the loot pinata, beat him or the world dies you know the drill" and more "this stubborn fuck wont listen to reason and is choosing to escalate" and throw in characters like Estinien, ysale and Hauchefaunt and you got a pretty traditional Final Fantasy story that not a lot of online games story updates can compare to.
Its just a shame Stormblood chose to divide their stories between two entirely different locations, styles and casts of characters. Were it just Ala Mihog with more zones and a deeper story about the refugees, rebels and collaborators i think we could have gotten a solid story and saved Doma for later.