I really enjoyed this book. It's got some heavier elements, like what we might call PTSD, loyalty issues, communication issues, Bad Guys, and some scary mothers with Mars issues. But there are still a few lighter moments.
The romantic sub-plot was weak, and if the relationship had been left to develop over some more in-universe time, it may have fared better.

Captain Zack is very much like Captain Reynolds. I'm hoping for some deeper character development in the next books. Particularly Deuce.