Distributed consciousness is probably an underutilized trope in SF--it's a lot of fun if done well. The best example I know of is Vernor Vinge's A Fire Upon the Deep, which included a doglike species where an individual was a pack. Ancillary Justice is centered completely on this concept, taking it to another level and exploring it thoroughly.
The novel is pretty much straight up space opera. There's some interesting social speculation here--the protagonist is a citizen (sort of) of the Radch, a galactic civilization that until recently was completely devoted to expansion. They are pretty ruthless about the process, but direct and fairly honest. At the time of the novel they have been stopped by the Presger, and our protagonist is working on the last colonizing "annexation".
The protagonist herself (gender is not a factor in the Radch, the default is "her") is an Ancillary, a person whose individuality has been removed and is now part of a group consciousness, usually a part of a Ship. Our protagonist is the sole survivor of this Ship's disaster.
I'd say the work is a little subdued for a space opera, but the exploration of distributed consciousness and imperialist social structures is worth the read. Have fun and think a little. Three stars from me.