I would rate the novel as mediocre. Although i still got movie to watch, but as far as novel is concerned it's bit of a overhyped. Sociopathy was interesting so was the story. Characters were different yet believable. But the overhyped rating and reviews got me so excited about the novel that when i finally read it....it turn out as average. I bet if someone read this book without any prior prejudice set by ratings and reviews, that person will find it amazing.
Personally ( my individual opinion) i found the story a bit stretched and Amy's confession quite unreasonable. Suspense and twist could be much better.
If you want to read the book...go ahead by all means. But, do not set any type of prejudice or expectation and It will turn out to be an interesting read.