I’m not sure that this was the intent of the author, but it strikes me that this would have been a fantastic middle-grade book. It tells a tale full of spooky things like liches, wraiths and minions, all set in a town of necromancers called Tombtown (located in a crypt). The tone is very light-hearted, with characters that I think many middle-grade readers would enjoy: the shambling, dim-witted minion Larry, the pompous and eternally optimistic Smythe, the self-important yet begrudgingly helpful snitch Usther, and of course the protagonist Ree, who has to shrug off the overbearing pressure of her parents to try to find her own way in life.
The story is pretty good, too. I think an argument could be made that a few too many things happen in the story, but it all moves fairly quickly to a dramatic, exciting end.
I think if you wanted to judge this book strictly as a “grown-up book”, you might find it a bit lacking. The characters could do with more depth, and more questions could be raised about the morality of everything going on in the town – there are references to things like cannibalism and bathing in blood which go well beyond “we dig up corpses to perform magic on them”. It is stated that the town has a bit of a laissez-faire, “just don’t make a big spectacle out of it” approach to killing, as well as suggesting that it’s OK to kill “upworlders” because most of them are adventurers who hate Tombtonians and want to loot all their artefacts anyway, but I feel like these are the kinds of explanations that suit a younger audience.
Overall, don’t expect a sophisticated horror/fantasy novel for adults out of this one, but for middle-grade readers (or “middle grade at heart” readers!) with high enthusiasm for everything Halloween, this would be a really good read.