I'm feeling generous, so 5*. It does build upon the basis of previous 2 books quite well. The already established world makes for a good substrate for characters old and new, and the plot itself is captivating. I admit that at first I thought the author is overdoing it with how extremely pacifistic everyone in the military was, but she sold the idea quite well by the end.
I also appreciate that all of the books were self-contained, so there was no second-book syndrome. That's not to say it doesn't matter where you start - the books do very much build on one another, so you'd be missing out on most of the context that seems to make each successive book in this series better than the last.
Plus, the plots of the three books make for a cohesive narrative arc that seems to open and close in the right places, showing us a tumultuous few years in the character's lives and the changes they effected.