TL; DR-Solid nature materials with a layout misstep. 98%
Basics- Who let the centaurs in the sub? Howl of the Wild is a character options book with new races, spells, items, and archetypes for characters who want a bit more animal in their characters. In addition, the book has a framing story about an expedition to uncover the guardians of the wild and the monsters they encounter, providing GMs with new monsters and story hooks for them to dig into.
Mechanics or Crunch- Paizo knows their math and it shows here. The new items, options, monsters, and characters all expand Pathfinder into fun new places. And the new grafts allow characters who are plain human to even get into the action. Some archetypes require the characters to have some animal parts, but with the right addition, anyone can play. It doesn't feel exclusionary, but lets people specialize into something new at the same time. The monsters are fun and bring some old creatures back into the mix as well. 5/5
Theme or Fluff- Howl of the Wild feels like it fits in Golarion and adds to it at the same time. I love the new races, and since its set far away from the main setting areas, they don't feel like they are tacked on. The new stuff all fits into the world and has fun descriptions and art to help you see what the authors wanted to add. I also enjoyed the story the book told as the explorers try to find the guardians of nature. They do, AND THEY ARE BIG. If you want some end bosses for a nature based game, here you go! 5/5
Execution- This book is good, but feels like a step back for Paizo’s normal work. What’s here is good. I like the flow and pictures, but this book doesn't have the short tables and descriptions of feats, spells, and items. It honestly makes it a pain. Also, while there are dividing pictures, the different sections are not as well defined. One change to a new subject was so jarring, I redownloaded my copy thinking I missed some pages in an error. I figured it out, but the older layout decisions are a better way to display the materials. I'd rather have less stuff and more tables to summarize all the pieces than too much to really take in. 4.5/5
Summary- This is a good book with a single error. I love the new crunch; it adds new character options and even tools for the GM to get to play with. These are all great additions to the game. I love the new story. It's fun to see a new part of the world and to see the new characters who live in it. It also builds out the world for the GM, so they can make new stories and monsters to challenge the players. My one issue is the layout. What’s here is good. It reads fast and easily, but the lack of tables makes skimming hard. As both a GM and a player, I want to be able to skim character feats, spells, and items quickly. Bring those back! But, overall this is a good addition to the world of Pathfinder. Check this out if you want to walk on the wild side. 98%
I liked the hybrid mechanics/storytelling approach, which also seems present in War of Immortals. It makes the usually dry activity of reading an RPG manual much more engaging.
I cannot really speak on the mechanics, but thematically everything is very cohesive. A very nice supplement in that regard.