If you've seen my selection of Le Guin's blog, you already know that while I respect her as one of the most insightful speculative fiction writers I've ever had the luck to read, her outlook frequently falls just short. This could be disappointing, but it's more important to look at the massive questions she does ask. This book is crammed with those.
The main issue raised in the novel is that of the differences between our visions of gender. Her foreword, which is a beautiful little piece about the use of fiction to frame real life, explains that science fiction and its cousins test our capacity for thought by contrasting what we think is impossible against what we cannot conceive at all. With a detailed explanation, it's easy to imagine someone who can transition between biological femaleness and biological maleness, and perhaps even exhibit both at once, but can you imagine someone who is psychologically a man and a woman at the same time? I don't know enough psychology to dispute which traits Le Guin identifies as feminine and which as masculine, but I give her all the credit I can for not pretending that women and men are the same people with different plumbing downstairs. I don't know about other parts of the world, but a lot of Americans have slurred this latter one together out of a strange need to justify civil rights. (Psst: Treating people well is not at all like treating them the same, and you don't need to make up an excuse to do so.)
Given a pretty good sense of what makes men and women different, Le Guin does quite a job of uniting these behind an alien mindset. This happens mostly because she shows it in the characters rather than describing it, for the most part. So while it's established here that competitiveness is primarily masculine and hospitality is primarily feminine, Genly the narrator cannot quite figure out what's motivating a Gethenian (as the aliens are called) in any given action. It's a function of Le Guin's subtlety that there's still an obvious, complex difference between Genly and the Gethenians that stems from the difference that while they are both male and female, he is only ever male.
Put The Left Hand of Darkness high on your list. It should be up there with Dune on the list of complex and intelligent science fiction creations.
The Problem
Since my main quarrel with this book is one of ideology, and didn't make me enjoy it any less, I'm separating it from my recommendation. If anything, it makes me like the book more for arousing the scrappy, perhaps competitive (heh) literary critic I wish I could be.
Taken as a whole, The Left Hand of Darkness turns into a panorama of wishful thinking. You may have read Orwell's Nineteen Eighty-Four, which envisions the result of a profound problem with human civilization. The Gethen Le Guin creates here is a formal inverse of the dystopia; it's almost Edenic, but its circumstances are not what would really bring about paradise on Earth.
The two main features of Gethen are its ice-age climate and its inhabitants' bisexuality. Genly occasionally chronicles the differences that have arisen between Gethen's civilizations as a whole and that of his own Terra (Earth). For example, from fighting against such bitter weather conditions, Gethenians have cultivated the value of permanence rather than our 20th- and 21st-century preference of progress and innovation. But then Le Guin drops the fact that although Gethenians murder each other from time to time, the planet has never experienced a war in its several millennia of recorded history. This is partly, as she says, because the weather is already so good at killing them, but also has something to do with never having learned violence as a result of their androgynous physiology. Most importantly, it is physically impossible for one Gethenian to rape another. A large part of the plot deals with the fear that Gethen's first-ever war will break out soon, but that quickly fizzles, both in terms of the plot and of the narrative's interest.
It's all as if Le Guin is saying that there would be no violence, neither war nor rape, if we were all sexually equivalent and if our planet beat us back rather than vice versa. These ideas were fun at the dawn of the 70's, around the time of the book's publication, just as they are now. But the circumstances are impossible. And to pin strife on theories of gender and ecological destruction distracts from the reality that greed and selfishness are demons we all have to fight. Just as there doesn't need to be an excuse for selflessness, it can be harmful to disguise that its opposite is not also an inextricable piece of human nature.