Very good. It won the Hugo and I for one agree with that assessment. This is Hugo-winner-quality storytelling.

Author Ann Leckie does do an interesting thing in choosing to use feminine pronouns for all characters, to emphasize the fact that the Radchaai language has no gender markers. For all that, though, the main character spends an awful lot of time worrying about gender because she has to speak other languages that do have gendered pronouns, and she is worried about guessing someone's gender wrong. I found that, for myself, it was sometimes difficult to know whether the characters were speaking Radchaai (and thus the she/her pronouns were neutral) or whether they were speaking Orsian or another local language (and thus the she/her pronouns indicated female). If they said he/him, of course, it was obvious. I would have liked a typographical cue, maybe having the Orsian dialog in a different font or in italics. But that's a nitpicky detail.

As interesting as this non-gendered idea is, though, it doesn't play any part in the story. It's fun, but not as clever as Delany's use of pronouns in Stars in My Pocket Like Grains of Sand. On the other hand, from clues (well, mostly from clues of omission) it appears the Radchaai have no socially defined gender roles and that there is no system of marriage (that we would recognize) at all.

The cover art has nothing to do with the story.