I have loved the Advanced Archetype stuff from Flaming Crab for a good long while. But I when looking at the “Letters from…” series, like many of you, had mostly thought "whimsical" when considering it. Nothing wrong with whimsy I say but not always to the quick with my pocketbook for it. But then I noticed that one of those products (this one) was labeled "World Tree" and being a longtime fan of the myth of Yggdrasil and the planar essence it adds to adventures I was immediately sold.
Again here I made a second mistake... because the product was neither whimsical (though there is a touch of whimsy) nor specifically about Yggdrasil. I am rarely so happy to be so wrong. It is a new (if familiar) myth, about a very SIMILAR tree but with its own origins. The material could serve as Yggdrasil, an offshoot or its analog. But also stands on its own.
And the crunch. I was not expecting that. So much. A religion about the dryad goddess of the tree with full Obedience rules (Like PFCS Inner Sea faiths). A fully developed PC race (with ARG buyout) having its own alternate racials, equipment, favored class bonuses (including classes from Advanced Class Guide and Occult Adventures and racial archetypes. Half a dozen monsters ranging from CR 2 to 24. Random encounters by the relative height the party is at in the tree, both relevant and clever.
All of that and still presented in a strong narrative frame with a clear layout, advice for adaptation, and a useable settlement with story elements for adventure. Even a great sidebar on adapting the material to other origins. Decidedly cohesive and well-thought. I applaud the team for delivering something so ubiquitously good and despise them a little bit because now I have to reconsider buying the whole damn series.
(It even has RATTATOSKIR so it pretty much won right there.)