I admit, going into this I did feel like it was a bit of a re-hash of The Secret History. In fact, the focus of this was entirely different. 
I'm still not completely sold - the author clearly wanted to focus on the second half of the story, and she does it very well, but it does leave the first half feeling somewhat neglected. I did really feel like Richard in particular was not very well characterised, and it meant certain parts later on in the book fell a little flat. 
But overall for a debut it is undoubtedly fantastically engaging and the scope of the book alone deserves quite a bit of credit.