The Left Hand of Darkness (1969)
Ursula K. Le Guin (writer).
Read in 2016.
Le Guin’s usual shtick of dressing up a good story and a good idea with a wealth of side stories and “side ideas”: fictive mythology, reasonable geography etc. It’s certainly soft SF, but of the right kind: Not flashy, and willing to use relativity, climatology etc. to good effect. Very thick and rich for its length and accessibility. Like Genly Ai, I find it miraculous that the Gethenians have any notion of evolution by natural selection, given the small number of species on Gethen and the huge disconnect between the people and the native species.