I'm curious to watch the film so I picked up the book when I saw it at some airport.
I'm still torn between "just a thriller" and "wow this is excellent". Turns out it got addictive pretty quickly and I liked the twists it took every now and again. Still, it just followed that pattern you kind of expected in the beginning.
Personally, seeing the couple's relationship develop was touching and actually pretty depressing at a time. Will our own relations eventually develop like that? Let's hope this is all just fiction and we can be better people and better couples.