I don't generally dip into YA territory, but I have been on a massive dystopia streak lately, and this book kept popping up on lists, so I gave it a try. I liked it well enough to read the sequel, Sapphique, and hope for a third book. The conceit is one of the most original I have come across yet; I would recommend it based on this alone. I had recently read Inverted World by Christopher Priest and found the similarities interesting. That's all I can say without giving away too much. The characters are sympathetic and for the most part believable. The world itself is fully realized and wonderfully imagined. I was slightly confused in the description of Incarceron (the prison itself), however. It is described one way, and then explained as another. The end tries to bring the two together, but I felt there was still some disconnect between what we are led to believe about it and what we find out it actually is. I would recommend this for 5th grade and up. Some of the themes are rather adult and there is some violence.