I did enjoy this but it's quite shallow. There are a lot of threads, one in particular I don't think was necessary, and I think with so much going on on the surface it was difficult to get the depth. 
 Ferelith had a fascinating backstory and the parts of the novel written in her pov were some of the most interesting, but for most of it she came across as a manipulative psycho with not a lot of redeeming features. In the first page she talks about how she knew that she and Rebecca would love one another, but I didn't get any sense of that closeness between them. I got no sense of how long they had been together, despite some of the entries being dated, and I was shocked when there was a sentence or two about how long it had been and texts they'd sent each other. And the ending was just so abrupt. 
 I liked the thread following the priest and the doctor. It was horribly fascinating and no doubt could have had its own book, probably already does. 
 I loved that Winterfold was loosely based on Dunwich. I remember going there as a kid, eating chips and listening to see if we could hear the bells ringing under the sea... ah, nostalgia! 
 Overall it's a quick read, compelling and thought provoking, I just didn't find it that satisfying.