Still the whole final
Amaurot dungeon and of course, the climax after for me.... it was utterly amazing. The scenery as that glamourous pinnacle of civilization burned and the very planet writhed in agony. The music (Mortal Instants). The horrible monsters as the Ancients' darkest fears were given flesh. Emet's sombre and sincere commentary of the whole thing.
And the scene after, as he dispatches the Scions without breaking a sweat, while the WoL finally succumbs to the corrupted Light - how close SE really came to making the WoL clock out for good, even if it was resolved by a literal deus ex machina from Ardbert (emulating the climax to FFVII Advent Children Complete to boot!). Seeing the WoL speak... with a voice... not their own... (and the big WHAM right in the lore with the WoL momentarily replaced by an Ancient destroyed a decade's worth of careful backstory crafting for my character instantly, my head was spinning from the revelation.). My heart was basically racing from the moment he opened the door in the Capitol and all those ominous flames shot out.
The only problem is that SE will have to pull all stops out to top this in Endwalker, but I'm sure they will succeed! 
Also, I have to mention still the scene early on with
poor Tesleen's fate... her transformation seeing exactly what happens when someone is turned into a sineater was shown in every gruesome detail (other than what happens when they're encased in that coccoon of feathers, probably for the best), and that there was absolutely nothing Alisaie or the WoL could do to stop it. It showed how utterly and totally broken the First really was, and I became even more determined to save what was left. Of course, cue the irony, with the WoL very nearly sharing that same fate (as mentioned above.).