In the third volume of this series, characterization and writing are just as strong as the first two books. Tregillis has really created a top-notch, well-crafted and plotted series that should appeal to a lot of readers.
That being said, I did have to take off a star, mainly because of the time travel premise. While this is perhaps one of the most well handled time travel plots I've seen, it still rubbed me the wrong way a little. It's my hang-up though, not the book's.