Pandaemonium done.
My immediate opinion is admittedly tainted by way of my P10 run involving both me and the other healer dying but the tanks--two Warriors--being completely capable of carrying the team to victory anyway, which is my least favorite way to win. But my non-spoiler opinion is... well, it's good to hear others like it, because I didn't.
This is the embodiment of 'fanservice not aimed at me'; in fact, its love of beating the Ancient fanservice drum directly made the story worse for me. Because Anabeisos actually has the exact one thing I desperately wanted from an Ancient story: Athena is the absolute embodiment of the sort of character that could've made me interested in the Ancients, right down to even having the powers I would've given a theoretical 'what if the Ancients were actually as terrible as people with that sort of power and worldview would be' fanfic character... only for them to instead cram her entire presence into one and a half cutscenes, with every minute of the rest of that story instead devoted to them desperately trying to sell Elidibus and Lahabrea as Good And Tragic Heroes, and cramming in the backstory for a rock that hasn't mattered for a decade and is only relevant here in terms of making Athena less interesting. Even cracked out the Persona 4 Piano for P11, and I'll tell you right now, that piano does NOT have the same effect if you don't feel that they've earned it.
I feel like if they cut Kokytus and instead gave Athena two boss fights' worth of exposition and opposition--basically, aping Eden's Promise even more than they already were--it would've worked a lot better, at least for me. But even that would've still had my least favorite element; the fact the story REALLY beats down Lahabrea, and then just... never gives Elidibus anywhere near the same treatment despite him arguably being worse. This time it literally IS the Elidibus we fought several times before, and I'm still not given the capacity to be mad at him?