I finished Ancillary Justice by Ann Leckie a few weeks ago but forgot to post anything here.
I enjoyed it very much, one of my favorites this year(along with the Sand Omnibus by Hugh Howey.) It's a bit confusing at first, there's no initial explanation about what an ancillary is, the main character uses the pronoun "she" to describe everyone, the story shifts perspectives and time periods and it unfolds slowly. But struggling to figure exactly what is happening is what makes the book so rewarding.
About halfway through the book I heard that there will be a second book, Ancillary Sword, so I was worried that Justice would not be satisfying. But it was and that is just one of the reasons it's an excellent read.