My favourite SF book this year was "Translation State" by Ann Leckie. It is set in the Imperial Radch world so having read the Ancillary trilogy is useful but not essential.

I like it because it contains the strangest aliens (the Presger) that I have come across. They are as far from humans in costumes as you could get. What the Presger do (and their proxies in the Human world the Translators) is totally unguessable.

A fabulous hard SF read and a must if you read the Ancillary trilogy.