This book is really entertaining to read and got me from the beginning. The fact that it is a psychological thriller and the narrative style reminded me a bit of Tana French, who I also like a lot. The characters are amazingly portrayed. 
 **spoiler alert** I have to say I loved the turn of events in the second part of the book, because I had completely fallen for Diary Amy, and really, I like the other Amy better. 
 What I liked the most about this book is the way it becomes an in-between-the-lines essay about the struggles of marriage and how every little thing can damage it beyond repair: the realization that the person does not understand you as well as you think s/he did, a unexpected move, unemployment... How everything comes down to: All's fair in love and war. 
 And I loved this quote: 
 "That ludicrous diary entry? I don-t need pathetic dancing-monkey scenarios to repeat to my friends, I am content with letting him be himself. That was pure, dumb Cool Girl bullshit. What a cunt. Again, I don't get it: If you let a man cancel plans or decline to do things for you, you lose. [...] That awful phrase men use: 'I mean, I know you wouldn't mind if I...' Yes, I do mind. Just say it. Don't lose, you little twat." 
 It is extremely interesting to me how this book - and as far as I know, other books by Gillian Flynn - presents the 'bad side' of women. How we can also be evil and murderous, contrasting with the romance-novel female heroine archetype.