Ancillary Sword (or you can try wiki's article, but its not much more helpful) is part two of the series begun in Ancillary Justice, which I very much liked. I liked this one too; though the effect wears off a bit, because there aren't many new ideas. This isn't really much of a review, because if you think you might like the book, you should read AJ first, and if you like that you'll definitely want to read this.
Many of the same elements are present, including the main character, whose lack of interest in telling male from female continues to be well drawn. In this volume, that extends to the (lightly touched upon) sex between various characters; you don't really know any of their sexes, or whether that matters.
Some way through I began to find the character's - well, the entire portrayed society's - obsession with tea a bit odd. It kinda brings out the all-stories-are-isomorphic thought, and connects the narrative back to Jane Austen or such.
The ship's crew - in the case of Breq's: the humans whose sense of fitness requires them to act as though they were ancillaries (i.e., as emotionaless unreacting pithed huamns controlled by the ship's AI) are also well drawn, and nicely fit into the story. There are quite a few bits like that, some that I noticed even if I can't now remember them, and some that I may have missed; but they all combine to make a fuller book.