I am in love with this book. The themes for archetypes are spot on and everything goes beyond horror basics, it's much more than vampires, werewolves, and zombies (though they are included). Some of my favorite elements are the Deep One corruption (corruptions in general are sweet, this seems like a well balanced mechanic for horribly warping the PCs into monsters, while still giving them a way to fight it) and the Gingerbread Witch. The Deep One corruption is a great example of the depth of horror this book includes, this plays on a less often used horror theme of the paranoia of harming oneself (in this case, by drowning). This reminds me so much of elements from the book The Boy Who Drew Monsters, and the mom's terrible fascination with people who drowned in a shipwreck a hundred years ago. You could adopt this same corruption for vertigo or even a bodily harm thing. On a lighter side, the Gingerbread Witch made me so, so happy. It's a well thought out archetype, I'm not sure they'd be great as a player character (but there aren't evil restrictions, so have at!) but I can't wait to insert a horrible Gingerbread Witch near some unassuming town, with her creepy haunted gingerbread house and evil delicious familiar.
I just can't say enough good things about the mechanics. They are flexible enough that you don't have to have a horror specific campaign to use elements from this book. The fear and sanity rules can be used with any campaign to add realism or more of a gritty fantasy feel. If your level 1 characters just killed a person for the first time, maybe they should lose some sanity and wrestle with that emotion. If they are in a dank, creepy dungeon with skeletons, maybe some of them would be spooked. The rules for adapting fear resistant characters like Paladins are also nicely balanced and I appreciate that attention to detail - your paladins don't have to yawn at the sideline, they're vulnerable too, just in a way less debilitating way that actually paints them as more of a hero around evil and undead.
Lastly, the warning about needing consent before using this book in a campaign was a very nice touch. That totally hooked me when starting to read this book. I kind of thought I'd just have spooky themed elements, but that paragraph inspired me to try to take this to the next level. How fun would it be to have a session that turns your actual living room into a haunted house, or to be the director of the scariest experience your friends have had all year?
If Halloween is your favorite holiday or you love low, gritty fantasy, I highly recommend this book. I will be reading this one cover to cover and am excited to use its elements for many, many sessions.