I've read a lot of stories with similar concepts. Its an ubiquitous formula: Sexy billionaire man + poor, down on her luck woman + sexy time = love. What I really liked about this book in particular was that this was the first story line that seemed fairly plausible. It was refreshing to see this basic concept perfected. I mean it's not reinventing the wheel by any means... but it's definitely putting on some shiny new rims. :) 
 Often the woman will always feel inadequate and dwell on it for the ENTIRE story. Low self esteem is really tiresome to read after awhile. What I liked about Avery was that yes, she acknowledged her life's differences from Nick's but she wasn't constantly bemoaning it. (view spoiler)[ For example, he whisks her away to Miami and instead of complaining that it's too extravagant and she doesn't deserve it, she actually goes along with it and is gracious. So refreshing. (hide spoiler)] The fact that her character had self esteem (although with a fair share of demons) allowed the plot to actually have action rather than just reading about some lady feeling bad about herself. 
 Usually the man will always be some alpha male who's seeking to completely dominate the woman's life but is written to be romantic instead of controlling/abusive. What I liked about Nick was that he wasn't as domineering as other lead males are. Is he a little high handed and bossy? Yes, he can be. However, he's not asking her to change anything about her life at all. She's not his prey falling into his predators den. It feels like they are two people getting to know each other and becoming friends as well as lovers. ::GASP:: Its so simple. I wish more romance equations had these nice variables. 
 To me at least, this felt more like a mystery story. Our narrator has a dark damaged past. We know that from the beginning. However, we never really find out what exactly that is until the very end. There's hints and allusions but nothing to really give the reader the full story. Both of our lead characters are holding secrets from each other and the reader. It allows the reader to search for clues along with the protagonists. 
 P.S. This ends on some pretty cliff hanger-y events. So I will definitely be continuing on with the story.