The Left Hand of Darkness is a really solid choice if you're going to read just one of the books I mentioned. And if you can finagle someone else into reading it, all the better! Definitely a good book to talk about.
Trust me, you're not missing too much if you skip Ready Player One lol
I wish I had been able to watch 2001 right after reading it. But from what I read about it, the book and movie were developed at the same time, though there are some differences, like the book featuring Saturn but the movie going to Jupiter because Kubrick didn't think they could make the rings convincing. After hearing about Hal my whole life, I was shocked to discover he was only in the middle third of the novel.