Some wonderfully intriguing concepts here and fascinating world-building, but ultimately the writing let it down for me. I couldn't figure out what the target group for this was supposed to be... it read very "young" to me, like lower middle grade, but the content, especially all brutality, seemed to indicate it's meant for slightly older readers.
I was also annoyed by the random switches from third person past tense to third person present tense and the occasional switch from limited third to omnipotent third - in some author's hands, this might have worked, but here it just came off, well, random. Characterisation, which started out decently enough, also seemed haphazard at times, especially with Tom's rather sudden change of mind.
All that said, while it was a two star book for me for most of it, the final fifth or so pushed the rating up for me and - together with the truly interesting world-building - might tempt me to read some more. It's a world I want to know more about, even if the execution didn't quite win me over.