Overall Thoughts:
Cahciua really stole the show here.
Some genuinely immersive locales (aided by the graphical changes). Conceptually, there were a lot of really interesting story ideas in here, but the problems were primarily in their execution.
The pacing was erratic and the story could have easily ended at three different points along the way. This felt longer than Endwalker. The dialogue felt overly apologetic in parts in an attempt to avoid stepping on anyone's toes. 'We know that you're harvesting souls from other societies to keep your immortality going, but we don't want to be seen to judge you on your cultural practices.' Some of the writing choices felt overly safe to the point of being awkward (i.e. it's high noon, but don't worry ratings board, they're just using rubber bullets). I also felt like the dialogue choices were definitely underutilized this time around, and missed having the usual banter line of choices (...Kupo?)
It felt like Daichi Hiroi wanted to create a grand scenario in line with Ishikawa's previous work without really understanding how the magic of her storytelling works. I think a more grounded, less ambitious storyline would have worked better.
End Speculation:
I'm not sure if I missed this in the information overload, but I'd like to know which shard Living Memory is in. Given that the problem is Lightning-aspected Aether, it's probably adjacent to a world with a Water-aspected Calamity, similar to how the Thirteenth's Flood of Darkness polarized the First towards Light. Given that the Tenth was rejoined in the Calamity of Water, and the Twelfth was rejoined in the Calamity of Lightning, my guess would have been something like the Eighth. Definitely an interesting plot hook, though, and I hope they expand on this partially merged shard more.
I also liked the Aloalo references.