Leviathan by Scott Westerfeld
I've been looking forward to reading Leviathan since I happened across a copy while browsing at Barnes and Noble. The publisher's synopsis is in this post and if you go to this page and scroll down you can see a really excellent trailer.
Leviathan is set at the dawn of the Great War, but in an Europe much different from our own historic Europe. In the world of Leviathan, Europe is divided between Clankers (powers that employ high-tech steam-driven machinery, ie. Central Powers) and Darwinists (who rely on fabricated animals created through advanced biotechnology pioneered by Charles Darwin himself, ie. Allies). The novel's main characters are Aleksandar, the only son of the murdered Archduke Franz Ferdinand, and Deryn, a teenage girl trying to pass as a boy and join the British air force.
I enjoyed Leviathan so much that I read it with conflicting desires: I wanted to get through it quickly to find out what happens, but I also wanted to savor it. I'm very much looking forward to the sequels (apparently Leviathan is the first in a four-book series).
I liked the characters. I thought the story was compelling (and that there was enough meat to it to nourish a series). I was fascinated by the world Westerfeld was able to create. And, I thought Keith Thompson's illustrations were wonderful.
Highly recommended. Russell is reading our copy now and then I'm loaning it to a friend.