I liked this, but I didn't love it, and over a month later I'm still not sure I can pinpoint why. But I'm going to try. This book definitely gets its creep on - there are a couple scenes that will stick with me for a good long while. The scene is set masterfully, and I'm absolutely transported to this household as it falls apart. It has mood and atmosphere galore, and I think the characters are well drawn.
I think the hurdle for me was that I've never been nearly as invested in psychological horror as I am the supernatural variety. Mental illness and the like don't freak me out, they make me sad. It's hard to be scared when you're reflecting on how devastating it is to care about someone who has crippling mental issues. I'm fully willing to acknowledge that's probably not going to be the case for most people. Nonetheless it was something I took to the table and it absolutely impacted my interactions with this story. If psychological horror, religious fervor, demonic exorcisms, madness, and family drama are things that interest you absolutely give this one a shot - it will likely scare the hell out of you. If, however, you're like me and those things hit a bit of a sour note you might want to skip this one. Your milage will likely vary.