The Ghost Brigades by John Scalzi

This book is a “sequel” to (or at least unfolds in the “same universe” as) Old Man’s War.  However, it can be read as a separate novel.

The story begins with Earth's interstellar government learning that three other intelligent races have made an alliance to wage a war on humans.  There is also a human scientist, Charles Boutin, who had worked for the military who is part of the plot against humans.  Boutin had used a secretly grown clone of himself to make it look as if he had committed suicide.  He is now with one of the alien races allied against Earth.

The human military has two sections.  One has somewhat modified humans.  The other is the Special Forces ("Ghost Brigades") - laboratory grown genetically modified bodies with augmented brains.

Special Forces makes a modified clone using DNA in the corpse of Boutin's clone.  They attempt to transfer an electronic version of Boutin's consciousness into the clone.  They hope this will help find out why he was a traitor and what he knows.  The clone wakes without Boutin's consciousness.  The clone, named Jared Dirac, is sent off to be a Special Forces soldier.

About half of the book is then about Jared's training and the first missions he's sent on.  This part is well written, kept my interest and introduces some interesting ideas.  However, I would say it was more than we needed to know about some things in order for the story to get from the initial presentation of the problem to the plot getting to a resolution of the problem.  The book is relatively short and therefore may have needed this "filler" to be novel-length.  Personally, I would rather it had been expanded in areas more directly involving the main plot.  As it is, it’s like a "stories pieced together to make a 'novel'" work.

In any case, eventually Jared begins to get memories from Boutin.  He comes to know somethings about Boutin, but not see specifics about the decision to betray humans.  When the military launches a mission to capture Boutin from an alien world, Jared is included in hopes he may have insights that will help.

Somehow, the military planners of the mission have not thought through the possible implications of the fact Boutin was deeply involved in the design of what is going with the soldiers.  The mission develops much differently than expected, a variety of previously unclear elements are explained and a few improbable elements get added.

I'm not sure how well this story will be appreciated by fans of military SF.  The story centers on the military and does involve some fighting.  On the other hand, it's not presented so clearly as a glorious business.  Nor does it strike me as fitting into a "blazing guns and big explosions" or "strategy military SF" niche.  There's a sense the military is needed, but questions are raised about its role in the big picture.  Issues are raised about the nature of the Special Forces and their lack of choice in being soldiers.  Missions are depicted that cause ethical unease, even if one sees them as the least-bad choice.

It's a lot about the military without a clear anti-war message.  So those strongly disinclined to military SF may find it has too much of what they don't like to be able to appreciate the book.

Questions about consciousness and identity are explored to some extent.  This arises in terms of Jared having elements of the personality from his experiences as a soldier and from the transfer of Boutin's mind.  It also comes up in discussions about an alien race who feel their minds are incomplete and seek to have fuller consciousness.

Personally, I found it to be a reasonably good read.  However, my preferences would have been for a book that spent more time exploring questions of consciousness and other ideas, and spent less time describing the life of a soldier.

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