Sucks you in with a mystery and delicious bad guys: the adults who control these kids lives. It was very compelling reading and difficult to put down, but ultimately not a story that I would re-read. The heroine, Echo, is frustrating because she never speaks or stands up for herself, though I guess the point of the story is that she eventually comes to do that. The story arc revolves around the Echo and Noah realising that the adults are not as one-dimensional or horrible as they think they are, but you can understand why the kids get that idea, when the adults are constantly wielding their power over them and making them feel helpless. At first I thought this was going to be a standard portrayal of fostering, where foster parents = money-grubbing abusers, and there's some of that. But by the end of the story, it's rendered more subtly than that. 
 Still, there were lots of things that bugged me in this story because they didn't ring true. For example, the school counsellor keeps telling Echo and Noah to trust her, but for a good long while doesn't give them any reason to do that. This struck me as off. If she's really such a clever Harvard-trained psychiatrist, she would understand motivation better than that and would give the kids some reason to trust her, instead of just saying "trust me" all the time. I don't know much about psychiatry, but the massive conspiracy between school, psychiatrist and parents to keep Echo from finding out what happened the night that she blocked from her memory seemed... strained at best. 
 Another thing that didn't ring true to me was the portrayal of high school, where the popular kids maintain their hegemony through constant scheming and meticulous image-management. It was so foreign that it was almost like reading a fantasy novel set in an alternate universe called Reputation. In my dimly recalled experiences of high school, the cool kids were cool precisely because they didn't appear to give a damn about what other people thought about them. (And because they were pretty / handsome.) It was at an intermediate level of popularity where people furiously schemed to maintain status, and that visible scheming prevented them from ever achieving the true heights of popularity. In general, human beings, whether teens or adults, are attracted to strong, independent people, and few of the popular kids in this story came off as strong. Rather, they were manipulative and terrified of losing status. Ultimately I didn't think it was a very fair portrayal of teens.