This is my favorite horror novel that I've read in a long time. I love the central story of Oskar and Eli, and although it's pretty clear from the start what she is, it plays out brilliantly. 
 I also loved the Swedish film, so was hoping for the book to flesh out the characters for me. It did that, and more. (It had a few new things to offer that I'd even consider twists.) Huge kudos to whoever wrote the screenplay, too, because while there were some things it didn't pursue, I think it encapsulated the book perfectly.