I read anything and everything
This is not simply one the very best scifi/fantasy books I have ever read, it's one of the best books I have ever read in any genre.
The Amazon blurb says: "When the human ambassador Genly Ai is sent to Gethen, the planet known as Winter by those outsiders who have experienced its arctic climate, he thinks that his mission will be a standard one of making peace between warring factions. Instead the ambassador finds himself wildly unprepared. For Gethen is inhabited by a society with a rich, ancient culture full of strange beauty and deadly intrigue—a society of people who are both male and female in one, and neither. This lack of fixed gender, and the resulting lack of gender-based discrimination, is the very cornerstone of Gethen life. But Genly is all too human. Unless he can overcome his ingrained prejudices about the significance of "male" and "female," he may destroy both his mission and himself."
That's part of what the novel is about, but, in essence, it's the story of two human beings who fall in love when they learn to trust each other and accept their differences.