Wonderful, fun finish to what is an awesome trilogy. I love the historical settings, the interesting people, the crazy science. Westerfeld did a great job.
Dylan/Deryn and Alek make a good team and they finish off their adventure in the same crazy spirit it started in. I liked the way the romance ended and that the story was more about action/intrigue than another irritating romance.
I totally forgot to add - *and* this series is so awesome it passes the Bechdel test!