If I had read this when it came out, or if the story hadn't been spoiled for me, it would definitely be a full 5 star read. Even knowing basically the entire plot, I still really enjoyed reading this book. 

Amy is a horrible person, but it's so easy to root for her. The author does an amazing job of making you sympathize with Amy, and all of the things Nick puts her through. Amy is also so incredibly smart, it's easy to see why she'd be so resentful of settling in such a dull relationship. 
But you also grow to like Nick, when you see how much Amy has done to set him up.