More of a list then an essay:
Ursula Le Guin: Left Hand of Darkness
Joanna Russ: Female Man Also, her short story "When It Changed" in Again, Dangerous Visions is magnificent.
John Varley: "Persistence of Vision" (Hugo winner)
Ellen Kusher: Swordspoint
At least one of the shorter, older Darkover books by Marion Zimmer Bradley since these books spawned a huge subgenre
Amy Thomson Virtual Girl
James Morrow's Only Begotten Daughter -- turns Christ mythology on its ear
Nancy Springer's Larque on the Wing -- intersting cover & take on gender issues---I really didn't like it but many people whose opinions I respect did.