Greer cuts through our absurdly patriarchal fantasies of romantic love, diagnosing the misery and anxiety they cause, and draws a picture of the female stereotype as castrated - a a passive receptacle for male sexuality. She also implicates capitalism in shaping and reinforcing patriarchy, with some great passages on the history of women in work.
There was far less visibility of trans issues and trans people when this was written and Greer's discussion of the female body in this book certainly has some dated aspects, but that doesn't stop it from being an important work in the history of feminism. It's also highly readable, non-technical and funny.