The prequel to this book, The Initiate Brother, was a vast, highly political book that succeeded through expert worldbuilding and a narrow focus on people. This book takes the relationships further, but with less success.
Russell has a lot to work with here - all those interesting characters he established in the first book, growing gradually more closely knit - and he does a lot with it. The individuals and their relationships remain a big draw, and Russell does an excellent job of showing larger events without ever losing his focus on the people affected by them. But the political side of the story simply went on too long for my taste. There's movement is more of troops than of spirits, and the logistical machinations take their toll. While Russell's choices are credible, after a while they cease to be interesting. This may be because he shifts his focus away from some of the action heroes of the first book, and more toward other, more social actors. Shuyun plays in both realms.
Disappointingly, Russell wraps things up fairly quickly (for a book this size), as if he recognized that he'd gone on too long. I'd have much preferred much less lead up, and a much longer winding down. That said, the books' central mystery is credibly explained, and Russell credits his readers with reasonable intelligence; there's a lot implied but unspoken, in line with the understated nature of the prose.
All in all, a good book and a good series. It's probably best read and purchased as a single volume. If you've read Russell's other (very good) books, you'll like this earlier work. If you haven't this is a good place to start. Recommended for anyone who enjoys subtlety in their fantasy.