Venat's character was the real hidden gem of this expansion.
Emet and Hyth were natural extensions of their Shadowbringers personas. Even a mere passing mention of Emet was always going to be well received. This expansion merely consolidated his S-tier status, especially now that he's been confirmed to be the long-suffering Y'shtola equivalent for your old team. Hyth was excellently fleshed out this expansion, but he was likewise a safe bet from the outset, given how positive of a response his bit part in Shadowbringers garnered. I really wish that there was a side-by-side picture of Yoshi-p/Foxclon with that in-game scene where Emet/Hyth read out the sales pitch on the next few expansions worth of ideas.
There are so many ways that they could have gone wrong with Venat, but they pulled her character off magnificently. While the few side-story snippets that we had of Azem from the time of Shadowbringers were really compelling, the difficulty with writing a character for the PC is that some players aren't going to buy into that persona because it's just not... them. Venat's writing circumvents this problem brilliantly by turning her into the resident trickster goddess and you her protégé. It's fairly easy to dismiss her character until you realize that she single-handedly made Hydaelyn interesting (in fairness, this is partially helped by the fact that Hydaelyn's beast tribe is an army of smol rabbits that are determined to help you whether you want them to or not). There's this brilliant moment where Emet notes in dismay that Azem 1 and Azem 2 are up to it again as you and Venat recklessly ride away on flying dogs, and it just feels... great.
I'm trying to think of a scene that matches up to Shadowbringers' showdown with Emet in terms of impact value. I think that it would have been easy to just try for a bigger and better final showdown, but they didn't need to in this case. For me, the real climax comes down to that showdown in Ktisis Hyperboreia, with Hyth's magnificent bastard gambit, and culminating with Emet's wry smile on the fade to white. Everything after is just denouement. So much rewatch value.
Honorable mentions go out to Hermes for being a compelling character.
It looks like pretty much any story that they write about your past life with the Convocation is pretty much going to be solid gold at this point. That ending screenshot of both your families converging and intersecting was icing on the cake.