Like all great books about war, this is actually about love, and loss. Purpose, and pointlessness. 
Like all great sci fi it is obviously about its authors present and recent past. In this case the Vietnam war, and also about stretching the readers mind in unique ways through reasonably plausible future possibilities. The technology is as always the backdrop for human relationships and societal organization. 
The feature of relativistic time perception allows for multiple human societal touch points and deeply enhances the isolation of combat veteran to levels otherwise impossible. 
How might society go wrong?
How might it go right? 
How might we stumble into war accidentally? (Like most of the time) 
How can you ask a man to be the last to die for a mistake? 
How can you ask him to order others to? 
5 stars. Loved it, recommend it to others, will likely re read.