It's no masterpiece. Writing isn't stellar and the characters could have more depth to them. It is an emotional book, but Mia's feelings doesn't at all times ring true.
I don't know if this can be classified as a D/s relationship, I am no expert, but the contract (the wording within) says to me Banks wants it portrayed as such? (All I really read was a guy that has a kink for dominance, don't make a Dom though. I could be wrong.)
If so, to me some of the scenes should never have happened. If Gabe is as immersed in the lifestyle as Banks want's us to think, he should really know better.
Just an observation/question... what does the cover have to do with the book?