What did I think of it? Well, to crib from (IIRC) Neil Gaiman, I think Jemisin must have been bitten by a radioactive awesome as a child, because OMFG that was brilliant . Brilliant worldbuilding, a believable set of societies, an ensemble of wonderfully realized characters (many of whom I wouldn't go out of my way to step on, in case they rubbed off), and...yeah. Oh, and this is a work of prose that begs to be read aloud. I was, I fear, occasionally annoying to metesten while I was reading it, because every now and then I had to share a particularly good passage with her. (These grew less and less frequent the further I got--not because there weren't as many good passages, but I wanted to avoid spoilers.)
What's it about? On the surface, the setup sounds a bit like EFP . You've got your halfbreed daughter of the onetime heir to the most powerful family in the world, raised in the barbarian North and summoned to her grandfather's court after her mother dies. There, she is immediately named one of her grandfather's heirs (along with her two cousins, neither of whom she has met before). The ensuing political intrigue is complicated by the fact that the most powerful family in the world got to be that way through their relationship with the most powerful god in the universe....
I would be remiss if I didn't point out that as a middle-aged straight white male, my reading was frequently interrupted by headscratches, sitting up and saying, "hey, wait a minute...." and the occasional facepalm. These were all good things; Jemisin did a superlative job of smoothly putting me into the head of someone whose life has been shaped very differently from mine, and suddenly making me see how (for example) the colonial narrative looks from the other side.
Recommended, and I'll be getting the next one as soon as it's out.
 OTOH, I don't think this is friar_bacon's tipple of choice, so YMMV.
 Extruded Fantasy Product. Derogatory term for generic Tolkien/other fantasy ripoffs, at least some of which don't really deserve it.