Ann Leckie's Ancillary Justice
I'm not even gonna TRY to explain what's going on in this book, b/c it's kind of complicated and I don't read enough sci-fi to be able to articulate it clearly. I will just say that I liked it much more than I expected to, thought the gender stuff was interesting, and liked the main character and found her mission compelling. Now I'm off to see what happens next. A-.