Ancillary Sword is the second book in the Imperial Radch trilogy by Ann Leckie. I read it shortly after finishing the first book, Ancillary Justice (review). Ancillary Sword is very much a sequel to Ancillary Justice - you definitely want to read them in order.
The bad news is that Ancillary Sword suffers greatly from "second book of three" syndrome, and perhaps also from being the followup to a huge award-winner. The story is on a smaller scale than the first book, it feels like little is accomplished in the story-line of the overall trilogy, and there's not much more revealed in terms of world-building. Even Breq's internal struggles don't seem to make much progress toward resolution.
The story in Ancillary Sword affects just the one planetary system, with only indirect mention of events going on outside. Breq's actions do make a difference there, but on a small scale - one section of a space station, a single opposing ship to neutralize, one abusive noble brought to justice. Compared to the empire-wide implications of the plot in Ancillary Justice, it seems like a big step backward.
The events in Ancillary Sword drop hints about a bigger conflict, perhaps involving another ship or two, and maybe an alien race. But none of that is resolved in this book. Presumably the third in the series will pick up on those threads. This makes Ancillary Sword feel like nothing but several hundred pages of setup for the next book, which is a common problem for middle-of-trilogy novels.
One of my favorite things about Ancillary Justice was learning about the world that Leckie has built. I expected that Ancillary Sword wouldn't have nearly as much new information, but even so I was disappointed in how little additional detail was revealed. The reader learns a decent amount about the Athoek system, but very little of that feels new - it's just a variation on themes already described in the first book.
I'm a bit on the fence about Ancillary Sword. It certainly has some major faults, but I enjoy Leckie's writing style and characters enough that it was still an enjoyable read. If the third book in the trilogy is as good as the first one was, then I'll be happy to forgive the "only a setup" feel to this one.