I read this as part of Halloween Bingo, so the fact that this book could reasonably be applied to about half the squares is woth mentioning. This is the first book I've read which used the singular nongendered they/their as pronouns, which slowed me down a bit at the beginning. But it worked, and never felt gimmicky. Z. was a plausible fourteen year old zombie who's entire family died in an auto accident: only Z reanimated.
There's werewolves and high school bullying and good teachers and bad teachers and a growing movement in favor of shooting all the monsters. As a metaphor, it is terrifying. But it's also the story of school misfits becoming friends, and of teens solving a mystery, so there is significant fun as well as the terror.
I'm delighted it was recommended to me, and I can't wait to read Shrieve's subsequent books. As good as this debut was the next one should be astounding.