I loved The Left Hand of Darkness.  Between her and Heinlein they rewrote the rules on sexuality and sex and gender in culture and society.

GooberMcNutly wrote:

It was The Dispossessed that turned me on to her, LHoD that got me even further in, then the dragon and cat books that drove me away again.

A poet in all her works though.

I saw her at a SciFi/Fantasy convention in Cleveland, OH about a million years ago, back when they were a celebration of the genius of the people who create the fiction and not fans celebrating that they're fans.  She was on a writing panel with a few others, I think Harlan Ellison was there too, and I was drawn to the preciseness of how she discussed the craft.  Witty and funny, sure, but it was like listening to a brain surgeon discuss their last operation in detail.  What I learned about writing that day was unequaled until I read Stephen King's On Writing, A Memoir of the Craft.