So far the stuff I like is that Empyreans can be fiends or celestials (shame this idea is so under used in the book, Arch-Hag should be Fiends or Celestials) I think the Empyrean Iota is my favourite monster in the book and I wish they had a Empyrean Iota Swarm. I do think Empyreans should have had reforms in their parents domain. And I don't like the change to the Empyreans damage type of its bolt, gives far less variety in the stat, but I like the inclusion of calm emotions, although it's weird on a Fiend (along with healing magic). I'll also note the Empyreans are the highest CR Fiends & Celestials making them the capstones for both types, a reminder that they should have just gone back to the Outsider creature type instead of Fiends and Celestials.
I like the Incubus/Succubi.
I like the new reveramts, especially the Haunted Reverant.
I like Mummy Lord, although it's alignment should have been "neutral", not evil.
Loved the Archpriest, but dislike the lack of a table to add species traits to NPCs.
I like adding spells to most Dragons, although I don't like the massive appearance retcon.
I don't like getting rid of templates.
I would have really cut down on the variants, many feel like they don't add in enough.
I like the new Swarms of like Manes, Dretches, Lemures, & Larva and again I will the Iota had gotten one. I would have liked mechanism to dial up the CR & Size of the Swarms, for larger Swarms. Zombies & Goblins should have gotten a swarm option as well.
I love the new Animal Lords, but I noticed they don't have the Titan subtype (and their default form is medium, they can in fact take on Humanoid forms medium or small, not just Huge or smaller beasts or hybrids), which is a contradiction from the Scroll of Titan Summoning which suggested they were Titans. I personally think they should have kept the subtype. I like that Animal Lord of Mice can take the form of a huge mouse or a Animal Lord of Hippos can take on the form of the Canadian House Hippo, aka a tiny Hippo. Third favourite creature after the Haunted Reverant.
In terms of Angels it should have been any Upper Plane, not Mount Celestia, Angels aren't just naive to 1 Upper Plane.
Don't like that the Genies are all looking like Dwarves, the art is great in the book, but the art direction at times can be terrible on occasion (not the majority of the time).
In the grouping section along side Angels, Devils, Demons, Yugoloths, Genies, Metallic Dragon, Chronatic Dragons, Beholders, Gobliniods, and Dinosaurs, Titans are their own group & the most diverse in terms of creature type, including Kraken (Monstrositie), Empyreans (All, so include Iotas, could we get more kinds of Empyreans in the future?, Fiend or Celestial), Elemental Cataclysm (Elemental), Tarrasque (Monstrosities) , Colossus (construct), Blob of Annihilation (Ooze). The common theme of the Titans isn't size, it's I guess being a semi divine creation. Colossus stat block was disappointing, despite being 2 CR higher then an Empyrean, the Empyrean would just absolutely destroy a Colossus. Colossus should have had a trait where the God who helped create it can speak right through it when they choose. I also think it should have had an aura that buffs allies.