This is one of those books I thoroughly enjoyed, even as I was fully depressed by the ending. It's probably expected going into the book, but there are twists upon twists upon twists. Most of them can be guessed early on, but the author does a pretty good job of misdirecting you to the point where you doubt your guesses. 
 This is a difficult book to talk about without spoiling for the next reader, so I'll say no more other than to say that I really like the development of the characters and I thought the relationships they formed were realistic--Gillian Flynn did a great job of infusing a low hum of doubt, in themselves and their loved ones. 
 The first half of the book is a true mystery, where I found myself unable to convince myself of certain players guilt or innocence. The second half of the book drops a big reveal, and becomes much more like a Dan Brown "mystery" where the reader is aware of all the players, and the story focuses more on wrapping up loose ends. Both halves are very entertaining, for very different reasons.