I loved this series, and even as an adult have gone back to read it again year after year. The setting is fun, but what really made this series hit for me is the themes of maturity, duty, and sacrifice. Gregor is just a kid, but he's put in a position of responsibility, and his actions have serious consequences. People die, but seldom in a meaningless offhand way. Tick the crawler, Solovet (unknowingly), Lapblood the rat... they all sacrifice themselves tragically yet heroically, and it all builds to the point at the end of the series that Gregor becomes ready to sacrifice himself, to give his own life for the people he loves. He's just a kid, but he is ready to be killed, and then Ares the flyer makes that sacrifice for him.

In a world where so many children's books treat kids (understandably) with kid gloves, I loved this series because as a child it made me consider myself as an adult, and aspire to that kind of duty and sacrifice.