Sometimes Science Fiction authors get hung up on describing the nuts and the bolts; the science and the technology.
Karen Traviss does not do this.
She does tell a good story, supported (but not carried) by the rich verisimilitude of the Halo universe. This book felt more real and more nuanced than its predecessor, Halo: The Thursday War. The characters had depth, the situations they found themselves in had gravity.
Staffan Sentzke is a well-rounded character. Initially, Traviss presents him as a terrorist, bent on revenge against colonialist Earth. But he quickly turns out to be more than that; a father and a family man, a wounded and injured man whose life was torn apart by ONI/UNSC. He may be the antagonist, but it's hard to side with or against him.
Naomi's struggle with the reality of her father is central to the book, but I think the rest of Kilo-Five steals our focus. Mal and Vasya seem like real people; the Huragok come into their own with the appearance of Sometimes Sinks. Even the Kig-Yar, between Sav Fel's self-serving actions and Chol Von's ambitions, prove to be complicated and borderline profound.
Even the AI, BB (Black Box) gets a little more complex.
tl;dr: If you liked Halo: Grasslands and Halo: The Thursday Way, you'll definitely want to finish out the unfinished business. And I believe you'll enjoy what Traviss has in store for you.