For me to review The Left Hand of Darkness at this point in time would be futile; what else could be said about it? It won its Hugo and Nebula Awards for good reason – by positing the world of Gethen, a place whose otherwise human-like inhabitants have no inherent sexual dimorphism, instead entering the state of “kemmer” during their monthly cycle, at which point any individual could potentially end up expressing any reproductive role. (So, for instance, you could impregnate a friend one month and then fall pregnant the next.)
This wasn’t Le Guin’s initial seed idea for the book – she wanted to depict a world where war was unknown, which prompted her to posit all sorts of other social structures and shifts, and eventually she decided that the way to go was to depict a world where gender isn’t a thing and sexuality is not a hallmark of identity so much as an expression of what happens to float your boat this month.
The end result isn’t perfect, and she would admit as much – particularly taking onboard criticisms that she chose to use the term “he” for all the Gethen (though it does mean she could say stuff like “The King was pregnant” to shake up readers’ preconceptions) – but in the midst of the New Wave of Science Fiction it really helped open up the door for other authors to consider such subjects in an SF context (or to use SF as a basis for their porn, but eh, not everything has to be high philosophy).