What a wonderful book!
It really puts magic back into magic, and not only when it comes to spellcasting. Listing my favorite things would be quite spoilerous, but please just know that I appreciate this approach to things like curses, beasts, feats, and everything else greatly.
This is the best book for Pathfinder, including all books for 1st edition, period. At least to my mind. Well done, wonderful job.
And those adventures - frankly, these are better than some (many?) standalone modules and AP chapters. There, I said it. Even the first one is already more complex, interesting and immersive, than most of "avoid traps and then kill them all" adventures.
The layout is really cool, but, even though at first I liked the idea, putting adventures and other spoilerey things (curses?) in the middle of the book is not very practical. I'd love to maybe try and cut some pages from the pdf and then show it to my players to let them see if there's something they'd like to use, and it would be much easier if all those things were compiled at the end of the book. I do think that more theme-focused approach to layout is cool, and I like it as well when I make stuff, but maybe just putting a simple blurb of an adventure at the end of each chapter with a reference to the page in the GM's part would be enough?
And, very last thing - I am all for including such short and "simple" adventures in literally every supplement. Please keep doing that. BUT, would it be possible to supplement them with a compilation of layered maps, like APs? Those maps are gorgeous (again - better than some AP maps), but I really hate to have immersion-breaking notes put on my maps in Foundry.
Quite frankly, in this day and age, the best thing to do would be probably to include a pack of high-resolution png files of the maps. People who like to print them could still do that, while VTT users would appreciate that.
Overall, this book is an absolute steal and almost a golden standard for how RPG supplements should look like. It's wonderful. It's completely my jam. And including short adventures using themes presented should become a standard not only for Paizo, but the whole industry.
Keep it up! I'm glad I'm playing Pathfinder 2e!