The good: This is an exciting story set in an original world based on Asian myths and customs, rather than the usual European ones. This gives everything, from the rules of magic to the political intrigue and caste protocols, a different flavor, and makes the whole thing seem fresh and new. Eon, rescued from the salt mines and used by everyone who knows her for their own purposes, is a fascinating character: a well-meaning girl whose entire life is based on lies and who is a danger to everyone she cares about.
The not-so-good: First, the plot is driven by the weakest device in the authorial bag of tricks: smart people behaving stupidly. It's just irritating to the reader when the main character keeps on making obvious mistakes. When readers can so easily see what's wrong and what's coming, they have to wonder why the character can't. Second, the last-minute conversion of one of the villains is not believable, even with magical intervention. And third, like so many fat fantasies, it sags in the middle -- some editorial tightening up would have been helpful. So the upshot is: it's fun and enjoyable, but could have been much better. It ends at a cliffhanger (another annoying author trick), so perhaps the sequel will be better done.