Based on a recent Buzzfeed article about underrated horror and the praise from Stephen King, I knew I had to read this book. Overall, I really really liked it, it was well-written and quite creepy, but I think the ambiguity is why it wasn't quite a five star for me. I'd definitely recommend it for horror / exorcism fans, but be prepared to be a bit frustrated if you like a neat ending. 
 The Good: In some ways, the book felt like it was written for me - nods to the classic and contemporary horror films, shows, and books I'm addicted to; enough self-awareness to use those references and tropes knowingly (and often with a wink to the reader); a relatively unreliable narrator (the memories of an 8-yo girl and a heavily edited reality tv version of events); and a bit of a feminist bent in the blog posts sprinkled throughout. I also really liked the way the book kind of spread the blame around - no one here was innocent, and there were plenty of characters whose motives we could only guess at, since we only know what Merry knows. Finally, I appreciated that most of the "possession symptoms" weren't completely over the top, which made it all the more unsettling. 
 The Frustrating: While I can completely understand why the author left the whole thing quite ambiguous - Was Marjorie possessed or just ill? Was Dad really the root of all the trouble? Was Merry being truthful but stricken with a slightly faulty memory, or was she purposefully obfuscating the truth? Who really was to blame for the tragic ending? And what does all the *oh noes cold* in the coffee shop mean? - it also was a bit frustrating for me. It certainly accomplished what (I think) it was trying to do, because I'm still thinking about it the next day, but it is something which does frustrate me in books.