Ursula K. Le Guin won the Hugo and Nebula awards for this book. I would have voted for it as well. Most excellent book. In the book she creates a cold world (Gethen, a.k.a. Winter) populated by hermaphroditic humans. Subtly, she explored the effect of sex on the interaction between people. Gethenians are primarily neuter. Once a month they go into heat. During that time, they can become either a male or female. During their lifetime, an inhabitant may become both the mother and father of numerous children. The apt line from the book is
The King is pregnant!
Le Guin tells the story from the point of view of the Envoy, Genly Ai. Genly is the first contact for this world. He represents the Ekumen of worlds, which hopes to add Gethen to its cooperative. First, he must convince the Gethen nation of Karhide. Palace intrigue sets him back, and his second attempt is with Orgoreyn. Factional fighting there prevents also Genly from convincing a Gethen nation to join the Ekumen. He is jailed.
The second main character is Estraven. He is the Prime Minister of Karhide. Unable to convince the King to join the Ekumen, he loses out and is exiled from Karhide as a traitor on pain of death. Rescued and living in Orgoreyn, he attempts to get the councillors of that nation to join when Genly attempts there. After Genly is jailed, Estraven helps him escape and they begin a daring trek across hundreds of miles of glacier to return to Karhide.
And thus I will end my plot synopsis, so as to not spoil it for anyone. The novel works on many different levels. As an adventure story. As a political treatise. As a study of the influence of gender. The characters are well conceived. The world is well-designed, with enough detail to make it interesting but not so much detail that suspending disbelief becomes difficult. The story is well-paced and about the right length. I ended it wanting more but not feeling like I had been short-changed.
I may attempt to pick up some more books of hers in this particular series.