TLHoD has some interesting concepts, but they are never used in an interesting way. A diplomat from a big, federationlike organization arrives on Gethen, accessing their readiness for entry. But things don’t go as planned, and the diplomat gets himself involved in domestic affairs. To add spice to her fabulated culture (and to the plot as well) LeGuin made the Gethenians hermaphroditic. Most of the time they are neuter, and for two days in a month they can be either male or female, dependent on their partner.
All this seems like a great setup, but it’s just that. The plot is underdeveloped and never goes anywhere interesting (and most of the time it’s a rather slow and boring walk). Normally this could have been circumvented by focusing on the characters, but those are equally underdeveloped. There’s never tension between the diplomat and his local partner, both remain facile character sketches throughout the book. Neither are the concepts around the Gethenians biology and their impact on culture explored in any depth, nor does the culture of the Gethenians feel more believable than a generic Star Trek race. Why this book has become a classic is a complete mystery to me.