I read it in several hour chunks over the course of a Sunday and it was everything she'd promised it would be. I had to pause in the middle to have a ten minute long ranting session at Chris about just how amazing it was. I don't want to give anything away, because I think going into it not knowing what to expect is definitely the best way, but there is a giant twist and I 100% did not see it coming at all. This is so unbelievably rare - I think the last time I had been so throw by a book was when I read The Thirteenth Tale a few years back. So that would have been enough to make me rave about it, but I also just genuinely enjoyed the writing style. The author made me care about the characters even though they were difficult to love at times.
Again, I can't really give you a plot synopsis or anything, I really think it's best to read without knowing anything ahead of time. But I really really super suggest that you go out and read it right away. Definitely before seeing the movie - which was good, but not nearly as good as the book (which is almost always the case, I suppose)