I was surprised at the amount of character growth exhibited by Castor and the other animals. Castor is used to surviving in the wild, with his pack, but being brought into the Unnaturals makes him examine who he really is. Pookie serves as a cryptic adviser, and the two read Charlotte's Web together. Castor even tries to convince the other Unnaturals to fight the system and remain true to themselves. The humans also learn more about the society in which they live and their place within it. This philosophy is balanced well against the action, so never slows down the book.
Clearly, this series will appeal to fans of Hunter's Warriors books, and I've even seen blurbs saying that it will appeal to Animorphs fans, although considering that no new books in that series have been published for almost fifteen years, I doubt there are many young readers who are familiar with those! This series promises to be a nice mix of elements: Dystopia, animals, and games as well.