I love Le Guin's writing for being social/philosophical/political/anthropological thought couched in sci-fi terms. In The Left Hand of Darkness, gender (or lack thereof) takes center stage. Winter is a planet where all humans are neuter, taking a gender only when they go into heat every month to mate. Societies on this planet are far from utopic, but they are rooted in a kind of equality we perma-gendered folks can't quite wrap our heads around. 
 I enjoyed the novel's ethnographic slant, which let me explore untranslatable concepts and idiomatic expressions (shifgrethor, nusuth, ...fixed genders). Characters struggle socially through misunderstandings based on fundamentally different expectations and worldviews. The focus on non-gendered people especially interested me, given the increasing number of real-life acquaintances I have who prefer to be referred to with the gender-neutral singular "they" pronoun. 
 The prose is clever. Wry at times, but rarely outright comedic. I appreciated the light touch she managed when considering gender issues from different perspectives - with a topic like gender, it might have been easy to slip into polemic.