I wasn't a huge fan of the ending, in which the solution was, in part, what I'd been thinking was the obvious since the first book. And doing this, and more, via a near-literal deus ex machina (as well as a more conventional "new tech saves the day") felt cheap.
But this is a minor point, and while this book was not as good as the two that preceeded it, the final third of the story continued to be thoroughly enjoyable.