This was part of a response I got today from an agent who had requested a partial of The Failed Apostle:
[F]rom a market perspective, the SF framework around the low-tech fantasy-like world is a tough sell–you need readers who like both SF and fantasy and the overlap between the genres is surprising small.
I found this to be a surprising statement. Perhaps its because I love a crunchy SF shell around a chewy fantasy center. Perhaps its because many of my favorite books fall into this slot–I’m thinking especially of Gene Wolfe’s Book of the New Sun, and all of LeGuin’s Ekumen novels. I don’t doubt the agent’s judgement of the market–she’s in a much better position to know than I am–but I’m still a little taken aback that this is considered a hard genre to sell.
(It’s also likely that you need to be really good to pull this off, and I suppose that it’s possible I’m not as good as Wolfe or LeGuin yet. I suppose.)