As an introduction to the world of steampunk and alternative history, set in a time period that doesn't get much attention (World War I), I thought this book succeeded. It certainly kept me reading, and the characters were entertaining. Knowing that it is the first of a trilogy, I can pretty much forgive the heavy-handedness with which the various machinery and creatures are portrayed. Any introduction into a world is going to be complex and kind of overwhelming. However, there were a couple issues I had with this book that I just couldn't get past enough to give it five stars.
Firstly, I thought the plot was overlooked too much in favor of the descriptions I mentioned. If you take the paragraphs about the machinery, the animals, and the surroundings out you are left with a barebones story that could be told in a few chapters. It's obvious Westerfeld put a lot of thought into the way the steampunk machinery and the hybrid animals would function and be used by military and civilians. But, especially since this is a trilogy it could have been stretched out over the three books, and the repetitive details about the Leviathan could have been cut - especially since the book is illustrated.
And secondly, I couldn't believe that the "Darwinists" could really develop hybrid animals with DNA strands and eggs the way it was portrayed. The "Clanker" machinery, yes - easily believable, if a bit ahead of its time as Westerfeld admits in the afterword. But just because Charles Darwin came up with the theory of evolution doesn't mean you can make an instantaneous jump from that to directly hybridizing and shaping DNA strands of animals for your own purpose. Not in 1914. It's a cool idea but it would have worked better in a futuristic setting, or if the technology was shown in its bare infancy.
Now for what I really liked:
The illustrations were wonderful. They captured the mood and feel of the book well and complemented the story. The old-fashioned captions added to the time period.
The characters were very well done, along with the dialogue. I liked seeing things from both Alek and Deryn's point of views. Though at times they seem a bit young for 15 and 16, most of the time they are well-rounded and interesting characters with unique personalities. I would've liked it if the entire book was about Deryn alone. Deryn is awesome.
The quality of the book is also great. It's very substantial and heavy with thick pages and color maps. Very steampunk and cool.
All in all - I'm going to have to wait for the next two books to give my final verdict, but definitely worth the read.