I wish I would have read the book but never got the chance. Based on the buzz and the trailers I was expecting a crazy psychological thriller like Gone Girl. And honestly it was kind of close to that. But it wasn't as intense. The movie was still a great watch and I really enjoyed the different way of telling the story that enabled the viewers to figure things out as the main character does. Emily Blunt was great as was the rest of the cast and the movie avoids dragging at any point which is really essential for a movie like this to succeed.
I would definitely recommend people checking this out. It was a very enjoyable watch but I would recommend not having your expectations too high to avoid disappointment.