She explores so many ideas.

Left hand of darkness explores our humanity through the lense of gender by removing gender from the society. It's an emotional exploration, and if you enjoy audiobooks the personal nature of the story goes well with the personal experience of it being told to you.

The dispossessed is probably my favorite book. It's more of a social / political exploration. You'll probably be thinking about it more where you'll be feeling about the left hand of darkness, so if you want something a little more externally focused and cognitive then it's a great place to start.

You can literally pick up anything she's ever written and have a great experience, but she's written some really hard hitters. Not in the sense of a baseball metaphor either. The story and the characters will just hit you really hard.