There are so many options that giving a strong answer is impossible. I’m willing to recant everything in here.
“Should read” as in “should enjoy”: either Terry Pratchett or Victor Hugo, pretty much anything from either of them. I’d throw in also Dostoyevski and Le Guin. Pick a book from them and utterly enjoy every word, the world, the people that populate it, the driving concepts that structure the narrative.
“Should read” as in “important information”: Chomsky maybe? Yeah, let’s say Chomsky, in particular any chapter of Understanding Power. Or maybe Washington Bullets? Also extremely informative. Or Why we’re polarized. I’ll stop here, there are just too many options. All of these are historico-political books, mostly about how the US politcs has evolved over time, talking about internal media and propaganda, US interference into other countries, and the creation of the two party hatred system.
I'll throw in Chomsky's contemporary Howard Zinn and A Peoples History of the United States if you want a better understanding of America. Fun fact, both Chomsky and Zinn worked on the version of "Pentagon Papers" that were read aloud on the floor of Congress. I'll also throw in a vote for Chomsky's Manufacturing Consent for a look at the way government and media work together to shape narratives.
For "should read" = "should enjoy", I would like to make a special mention of "Wuthering Heights" and "Villette" by the Brontes. I had a completely different experience from reading "Wuthering Heights" in my thirties vs when I read as a kid. The book's atmosphere and the characters left a deep impression on me. Also, "Ivanhoe" by Sir Walter Scott. That book is such fun to read! Another one, "Demons" by Dostoevsky. A book that is interesting as well as slightly disturbing.
Solaris by Stanislaw Lem. A captivating exploration of the human psyche. Deeply philosophical, eerie and romantic at the same time. It's one of the most unusual science fiction books I've ever read.
I read it, maybe the translation I had wasn’t great, but it barely left any impression at all. Nice, but little else.
I read the German translation of the book years ago without knowing anything about it. So I was expecting just another science fiction story and was surprised at the strange direction Lem takes. Maybe that's why it stuck with me.