I have to admit, this book isn't really written with me in mind. I am not the demographic that this book is targeting, so the low score is partly reflective of this fact. I have many students, however, who would and do love this book, and I can understand their enthusiasm. The subject matter is exciting -- dark and gritty. The main character is sarcastic and flippant. The two main characters steal a toilet, which always goes over well with teen readers.
I felt that the most successful part of the book (which is also reflected in the author's statement at the end), was the climactic scene. The serial killer character is really gross and scary, and Duncan, our main, is fighting for his life as a subway train comes rumbling toward him. Graham McNamee admits that this was the scene that first inspired the rest of the book, and it shows. There were also powerful, surreal moments when we see Duncan struggling with trauma via nightmares and hallucinations, and those work well.
But there were other portions that were face-palm bad. At one point, Duncan tries to tell the cops about the serial killer. I have never seen cops painted in such a negligent, incompetent way. They don't take his information. They don't even care about the situation. Without giving too much away, I just remember thinking, "Yeah, right. The cops won't help you. Ooookayyyy." I understand that the novel hinges on the premise that Duncan, as the protagonist, has to find the serial killer himself, but that hinge is weak. It is also hard to like Duncan at points because he has such a hero-complex. He thinks it is his destiny to save the woman the serial killer is targeting, but this gets old so fast. There aren't really repercussions for his narcissistic want to be the hero; he is never humbled. He gets banged up a little and his life moves on, presumably towards other heroic acts. What a knight in shining armor.
TL;DR: I completely understand the TV drama appeal of his book, but I'm a little over it.