I'm only going to list books that are legitimately fun and (mostly) easy to read. All of this is obviously IMO.

Gogol is extremely funny and the most fun, interesting, and creative of all the classic Russian writers. The Overcoat is obviously really good but you really can't go wrong with anything Gogol wrote. The Government Inspector, his short stories, Dead Souls, they're all awesome.

Lovecraft is fun, interesting, and weird. Yes, he's a racist, but he has a socialist redemption arc. At The Mountains of Madness is amazing.

Octavia Butler is fun, easy, and disturbing. Kindred is great, Parable of the Sower feels like it was written yesterday although it's thirty years old.

Zola has been recommended here a few times, I've read a bunch of his books and really like him a lot. He's always really concerned with the French working class in the 19th century. His issue is that he libs out whenever things get really interesting. Germinal is a legitimate classic and the movie is on Amazon Prime and is arguably better than the book. L'Assommoir is also really really good.

Ovid was recommended already, check out the imagist translation by Charles Boer, it's pretty wild. Virtually any translation of Homer is also awesome. Gilgamesh is also really great. This shit has been around for thousands of years for a reason.

A Grain of Wheat by Ngugi Wa Thiong'o a great anti-colonial classic that was recommended to me here. Pairs well with Bao Ninh's The Sorrow of War also recommended here, about the Vietnam War from the Vietnamese perspective.

Paradise Lost is absolutely beautiful, really fun and interesting, obviously not the easiest read. I picked up an edition that has a ton of great footnotes so I recommend finding one like that if you can. It's basically like if Shakespeare was a hardcore fucking nerd who was way more educated but also trapped in his house for years malding over his side losing the English Civil War.

Joyce is truly wonderful but really makes you work for it, at least with Ulysses and Finnegans Wake. I've only read a few pages of the latter; the former is a lot more understandable if you pair it with the various books that have been written to explain it, which are almost classics in their own right (Stuart Gilbert, Richard Ellmore—there's another book out there, I can't remember the name, that does almost a line-by-line explanation for Ulysses, and as it turns out, shitloads of the book are basically references to Irish ballads, because Joyce was also a really good singer and his whole family was obsessed with singing). Although actually there are still many large sections of Ulysses which are almost incomprehensible. Dubliners and A Portrait of the Artist are obviously much easier and more approachable.

Romance of the Three Kingdoms is a Chinese classic that is a huge deal in East Asia, is really fun and wild, though virtually unknown in western countries.

Marquez and Shakespeare have already been mentioned, but definitely check out Kozintsev’s Soviet adaptations of Hamlet and King Lear, they’re amazing.