Halfway Human - Carolyn Ives Gilman
When I rate science fiction novels, I rate them relative to others in the genre, and this is definitely well up there. The basic situation, as it's revealed over the course of the book, doesn't have much subtlety, but the importance is in the details, and that is where the nuances come in that are worth thinking over. Gammadis is one of the more intriguing science-fictional cultures because Gilman's construction of it is so detailed. Capella isn't quite as vivid, but she spent some time developing it too. Plus, Tedla is such a well-drawn character.