Ostensibly, the novel is about a traveler to a far world, called Winter, seeking to bring this world into the interstellar fold. This interstellar civilization always sends a single person to begin contact, progressing patiently, letting this new communication develop. The world of Winter was settled by human millennia ago, the planet turning to glaciation in the intervening years. What makes this particular planet unique is that the inhabitants are non-gendered, having both gender organs, but being that gender but a few days per month.
As speculative fiction goes, this novel is all speculative. There is relatively little science in the novel, but there is great exploration. LeGuin does not head boldly into this exploration, but gently, using her considerable storytelling prowess to live through this strange place, through the eyes of a strange person, in a strange society, in a strange time. And yet, despite this enveloping strangeness, the humanity of each character emerges, the world emerges, the facts emerge, with few lectures and many examples.
When I was young, I saw this titles on the shelf for many years, knowing that I liked LeGuin, yet very ambivalent of its description. That was shrewd, for this novel would have been completely beyond me. In high school, much of it would have gotten away for me. Even now, I find myself below this work, rather than above it. Its complexities are beyond me. By all rights, this novel should have been a tedious train wreck, but it works at a deep level, engaging you on a level that few modern novels will. Unlike many SF works, this one is based on humanity, moves with humanity, and concludes with humanity.