I read this novel in one day, which is always fun for me. It helped that that one day was the day that daylight saving time ended. 
 I shelved this as "scary" based on reviews I've read online, but I didn't have any trouble walking through my dark house after I'd finished it. The themes were so similar to those in other books I've read recently that they felt more cliched than shocking. Like Camille, I avoid going to the geographic area where my family's from because the intractable depression and hopelessness of the culture there literally makes me ill (not for the exact same reasons Camille's hometown makes her ill, though. Just so no one gets the wrong idea). Visiting there is scary, but not "afraid to turn out the lights" scary. It's more "there's no escape because these people and I are the same species" scary. More "this is how most of the country and probably the world is" scary. It's not an entertaining scary, either in real life or reflected with emotional accuracy in fiction. 
 Flynn wrote a rich internal life for Camille, and all of her characters were distinct, but the ending was a big blurred rush. One could argue that that's how Camille experienced it, but I found it unsatisfying as a reader. It didn't seem to match the pace and detail of the rest of the novel. 
 I did like it better than I liked Gone Girl, though.