Well, it's close to fantastic. On one hand, the description of a family coming apart at the seams, and a teenage girl being lured into an emotionally and potentially physically abusive relationship with a predator are, for the most part, gripping and realistically written. The main character, Ames, has reactions that feel mostly authentic to me, even as I find her a bit of a whiney brat to start. But I get that she would react that way (how dare her mother shut down her iTunes account!) just like I get how Marc can lure her in so easily.
That said, some of the family reactions just don't make much sense. Ames's mother does such a complete 180 from loving, attentive mother to disconnected and uncaring mother so quickly that it strains belief. And the relationship with Marc is (necessarily?) rushed, packing way too much into the last 75 or so pages. I'm not sure why Giles felt the need to pack Marc and Ames's entire relationship into what's actually just a few days, especially considering what Marc ends up asking Ames to do.
Because Giles takes so much time documenting how the family was falling to pieces before Marc ever shows up (something like half the book) that ends up being the main attraction, and not the relationship. ("Romance" is not an apt label here.) It's a quick read, and mostly absorbing, but there are some flaws in pacing, timing, and characterization.