I like Terry Pratchett a lot more than I like JRR Tolkien.
I know that's an odd way to start out a review of Ann Leckie's Hugo Award-winning hard science fiction novel 'Ancillary Justice', but hear me out. The reason I like Pratchett more than Tolkien is that I always felt like Pratchett started with a story, and did about as much worldbuilding as he had to in order to explain the bits that were important to the story. Whereas Tolkien, I felt, really had much more interest in the language, history, culture, geography, et cetera, of the world he created--the story was really just a means to show it all off.
Some people love that kind of immersion. They want a world so real they can imagine inhabiting it, and can return to it every time they read the novel. Me, I'm not so much into that. I like to read a good story, and see worldbuilding only as a means to the end of telling the story you want to tell. This isn't to say I can't appreciate the craft of worldbuilding--Tolkien is a great author and I'd be a fool to say otherwise. But I know which one of the two I read for pleasure.
I think that's why, despite appreciating 'Ancillary Justice', I didn't really enjoy it all that much. There is a plot, and it's actually a very clever one. But Leckie takes a lot of time in getting to it; she's got a lot to say about the Radch, the empire that controls vast segments of the galaxy, and she wants you to really get a handle on the reality of living in the empire they've created. Vast chunks of the novel are taken up explaining customs, linguistics (yes, including the bit the book is famous for, that the default gender is "she") and politics of the Radch, long before the plot ever kicks into gear.
(It should be noted here that it probably doesn't help that half the book is an extended series of flashbacks that alternate with the main action. I can, to some extent, understand exactly why Leckie did it; the opening sequences, of the main character traveling to a distant ice planet in search of the tools of revenge against the woman who killed her...well, most of her...it's a great hook, and it would be hard to abandon it. But it does mean that there are two interweaving plotlines that both take a long time to get going, rather than one plotline that climaxes at the mid-point of the novel and another at the end.)
Still, for all I complain that I'd prefer more plot and less worldbuilding, the worldbuilding we do get is choice. The Radch has some wonderful thematic echoes of late-period Roman Empire, but there's a lot going on under the surface that's more reminiscent of the British Empire towards the end of its heyday, when people were just beginning to wake up to the idea that "loot and pillage other countries to civilize them" was not exactly the moral high ground it was once seen as. There's a lot here to reward careful reading.
There's also an excellent sci-fi conceit; the Lord of the Radch, Anaander Mianaai, is actually an intelligence spread out over multiple bodies throughout Radch space, ruling directly through thousands of host bodies (much like the main character did at one point before her core intellect was destroyed). Leckie does a lot with this concept, and every development of it is both interesting and proceeds logically from the one before. By the end, when the plot finally gets to gallop, you're definitely left wanting more.
That may, I suppose, also be seen as a weakness; this book does a lot of worldbuilding to set up the next two books that presumably will shake up the systems established here. But as I say, it is excellently-done worldbuilding, so fans of that kind of SF/F are going to have a lot to like. Me, I wasn't quite so enamored of it, but I can certainly see what all the fuss was about.