I was excited to read this, the 8th of the Temeraire books, because I so thoroughly enjoyed the first seven books, (possibly excepting the 6th, which I don't remember making a big impression when I read it 4 years ago). I was disappointed by this book though, and I've been trying to put my finger on why.
I hit upon my answer when I compared it to the other books in the series, which thus far has been doing two things: 1. Telling the tale of the Napoleonic Wars with dragons and 2. Showing how various different cultures interact with their dragons in different ways.
The books of the series cover the following cultures:
Book 1: Britain
Book 2: China
Book 3: Turkey, parts of continental Europe
Book 4: Southern Africa (modern day Botswana and South Africa, approximately)
Book 5: Britain (with activist dragons this time)
Book 6: Australia
Book 7: Inkan Empire, the Amazon (briefly)
Book 8: Japan, USA, China (with extra intrigue this time), and Russia
When you look at this list, the problem with book 8 becomes immediately clear. Novik tries to do justice to 3 new cultures and tell a continuing story in a culture that has already been introduced, where usually she focuses on just one or two at a time. The result is unsatisfying. The characterization of the Japanese dragons and the American dragon (who trying to open up Japan to trade 20 years too early, only 6 years after the Louis and Clark expedition happened in real life) relies far too heavily on stereotype, and not enough on carefully reasoned reimagined history. The Russian dragons are given hardly any page time at all, even though they have the most relevance to the Napoleonic Wars part of the plot.
On top of visiting too many countries in one go, Novik gives Laurence, the main human character, amnesia. Why? Well, it isn't to examine the feelings that go with a debilitating setback, or explore how amnesia works in real life, because it's classic Book/TV Amnesia ( http://tvtropes.org/pmwiki/pmwiki.php/Main/EasyAmnesia ). It isn't to help the reader remember what they read five to seven years ago when the first few books came out, because it actually hinders the reader's ability to remember the previous books. Laurence doesn't spend much time being reminded of what he's forgotten, so mostly it is him not remembering something and if the reader doesn't remember it either, well tough luck. It isn't to revel in the amnesiac lover trope ala TV Tropes ( http://tvtropes.org/pmwiki/pmwiki.php/Main/AmnesiacLover ) (which I wouldn't have minded) since Laurence spends most of his amnesiac time hiding among strangers, not with Temeraire. And it isn't used in any novel and interesting way that would otherwise justify it. So why does he get amnesia? I don't know. It is incredibly pointless.
The whole trip to Japan is incredibly pointless and doesn't further the plot. The character they pick up in Japan spends a long time doing nothing. Then he decides he must fight against China, even though the Japanese and Chinese weren't mortal enemies in 1812. (Japan was closed to foreigners, except for trading sporadically with the Chinese and Dutch. The start of Japan's modern conflict with China wasn't until the late 1800's not the early 1800's).
It would have been a better book if it had focused on properly reintroducing the characters they meet in China and showing how Napoleon is avoiding the fate of having his army freeze to death in Russian winter. Russia really should not have been tacked on like an afterthought. Hopefully book 9 will do better.