You know, when you write something that generates praise like, "though I can't put my finger quite on why, this book felt surprisingly unique within the genre," you know you are in the realm of Beyond Easy Categorization. There's nothing wrong with this (presuming one exists outside the traditional-publishing matrix), but it does mean that people looking for a neat categorization might get kind of stymied. So in addition to the "60's social sci-fi" thing, I have updated the Amazon, et al. tags to include the Futures Past and Present categorization as "anthropological sci-fi."
No idea if this is a category with traction, but LET'S EXPERIMENT! 'Tis what this is all about!