I read this a while ago and loved it; reread it this week for a book discussion. (And then neither of the kids who came finished it. Why do I bother?) It still held my interest the second time around--Westerfeld created a pretty solid, intriguing world here. 
 Unfortunately each book gets a little less good after this. I'm killing the book discussion group and not bothering reread the rest of the series. I know it'll only end in disappointment anyway.