(copied from Amazon review)
My impression of this book from marketing was that it was going to be a sci-fi erotica. The author (in a blog entry) talked about exploring the "Aphrodite archetype" in a world where sexuality and sensuality are accepted, comfortable subjects. Much like the short-lived "Firefly" TV series, courtesans are high-status artists who are a little bit therapist, a little bit diplomat, and a lot sexual artist.
I like erotica quite a bit, but I was pleasantly surprised to find that Cythera is more of a 1960s/70s-influenced sci-fi adventure: Cythera and a delegation of diplomats are escorting a young, naive treaty groom (Hereu) from a sex-segregated society to his wedding on another planet (Agni), in order to end the war with Agni. Lots of political factions from Agni don't like that, and are actively working to impede it, in both political maneuverings and space fights.
There's also a romantic subplot, between Cythera and a widowed starship pilot (Athain), intertwined with a lot of the erotica. The lovely (dare I say feminist?) romance of equals, well-established in their careers, for whom there's never any conflict between career and romance, also contributes to the classic sci-fi feel.
Things I loved: all the characters learn from each other--it's not just the Wise Courtesan teaching the naive virgin about sex. Cythera makes mistakes and has things to learn from Hereu as well. The world-building is impeccable and engaging, especially for such a short work. The behind-the-scenes looks we get at the work it takes Cythera's temple to build erotic fantasies makes the erotic scenes themselves sexier and more grounded in reality.
Things I hated: Well, I wished it was about three times longer, with more plot and room for character development and interaction. It *feels* like the novella it is, complete with pacing problems. Graham does well in building coherent narrative and character arcs out of a handful of events and interactions, and the slow, luxurious world of the temple courtesans contrasts well with the hurry-up-and-wait space travel. But I still felt like the plot and the characters could have used more space to expand and breathe on the page, even with a fast-paced plot that only covers the span of a few days.
Overall: if you like classic sci-fi adventures with female protagonists, this is a great choice, even if you're not the biggest fan of erotica. If you like erotica (especially featuring exhibitionism, some light S&M, and a little humiliation) with sci-fi plot, this is for you. If you like political sci-fi and world-building, this is for you. It's definitely already on my re-read list!