Ok, so I went to a college where we basically read books for 4 years, so I've read a decent chunk of the classics. I want to mention before I forget to that everyone has different opinions on which books are good. So the ones I'm going to suggest aren't necessarily going to be up your alley and you might really love a book that I despise. Now, onto the suggestions:

My all-time favorite book is The Iliad. It really doesn't get better than ancient greek epic poetry. That being said, don't start with this. It can seem a little dry until you're used to reading dry things. Should you decide to attempt it, read the Lattimore translation and for the love of all that is holy, just skip right over the catalogue of ships when you get there.

Oh, I should definitely recommend Grapes of Wrath and Catch-22. In high school I went through a "I have to read the classics to appear intelligent" phase and it was mostly a huge failure. I couldn't get through Don Quixote, Moby Dick, or any of the many Shakespeare plays I started. (Except King Lear, that one was dope!) But Grapes of Wrath and Catch-22 were actually exciting enough to keep my attention. Catch-22 in particular I'll never forget. I'd heard about it, it's a very famous book, and I was expecting it to be dry and "deep". But it wasn't, it was utterly hilarious. I laughed so many times while reading it, it was just a silly romp with some war or other happening in the background. Until the last chapter, when the whole damn book gets recontextualized. It's a masterpiece, is what I'm saying. And suuuuper easy to get into.

Other books that are good, let's see. I really liked Middlemarch. George Elliot is like a better Jane Austen. (Also, despite her pen name being "George", she was a woman.) I responded to you elsewhere about War and Peace, it's really good. Someone else mentioned Candide somewhere, I agree. It's funny, short, and makes fun of Leibniz. Classic. Someone else said Heart of Darkness sucks, hard disagree, I really liked it. It too is short and Conrad is fantastic at painting a picture with his words. Also, English is not his native language, so it's doubly impressive. I know I said earlier I couldn't get through Don Quixote in high school, well, I read it in college and actually really liked it. That's not quite true; I hated the first half and loved the second half, so I'm a little hesitant to recommend it. I just felt bad for the guy in the first half. It is pretty funny though and apparently even funnier in spanish, lots of untranslateable puns and shit.

Now there are some other books I wouldn't necessarily call "classics" that are good. Dune, for example, although the characters are really just cardboard cutouts. But the world-building is amazing and it actually really works because it's sort of the founding myth for a civilization. Oh! How could I forget Charles Dickens? A lot of his stuff is good, but I'm going to recommend A Tale of Two Cities. Yes, it's like his most famous book, but I think there's a reason for that, it's damn good. Really makes you feel for the characters. Also, if you've never read The Hobbit or Lord of the Rings, do that. Sure, the morality is a little black and white for my taste and there are hints of racism with how the humans from the south and east are portrayed, but still, it's a good time.

And lastly, I will never not recommend anything and everything by Ursula K LeGuin. Most especially Left Hand of Darkness. And if you're feeling up to a little philosophy and political theory sprinkled into your sci-fi adventure, The Dispossessed is super fucking good. In a similar vein (although I like him less) you can't go wrong with Asimov. His Foundation series in particular is quite good.

Ok, well, now that I've basically written a novel for you to read, I'll stop. Good luck in your reading adventures comrade! And if you ever just don't like a book, stop reading it, even if other people think it's life-changing or earth-shattering or whatever. Not every book is for every person.