Spoiler-ful advice to SE's Writing Team for Future Content.

[Brannigan]

Stop killing off your villains after giving them barely enough screentime to register them as mildly interesting. For example

-Gaius' whole crew sans Nero. Even in 1.x, Gaius was underdeveloped compared to Nael. Gaius in 2.x has like two interactions with the player before he's dead.
-Hydrus. Dumb death. Felt forced because of the separation between MSQ and primal quests this expansion. He, at least, has more interaction with the player than others, but it still felt like it wasn't that much.
-Pope died at the end of Heavensward. Nidhogg took a while. We didn't really encounter them more than a couple of times each. The Heavens' Ward clearly had some personalities based on their in-battle dialog. Unfortunately we only interact with like three of them for the entire expansion. I guess we hate spear-of-light-thrower guy because he's kind of a dick and killed our buddy.
-Various ascians like Nabriales and that-chick-who-fused-with-Lahabrea.
-Warriors of Darkness - l o l

At least Elidibus is still alive. Lahabrea had a good run, too. To be fair, they do this with good guys as well - it was painfully obvious that scarface was going to disappear at the end of the terrible Alexander storyline and "special eye" catguy was going to go away at the end of CT. Sky Pirate man didn't disappear, but he's not really that important of a character in the grand scheme of things. Did Caith Sith go away? I don't even remember.

Their most developed villains have been Nael van Darnus (rip) and Nero. Nero's working with us right now, which is good, cause I bet he's gonna go rogue (again) in the expansion. Uh, if he didn't already. I don't remember if I finished the MSQ or not.