Any particular genres? My favorite director is Tarkovsky and I don't think you can go wrong with any of his films. Stalker would be a good place to start. Though my favorites are Mirror and Solaris.
Be forewarned that his films are very long and slow paced most times. Many find his films boring and even I get bored watching them sometimes. I have to be in the right frame of mind to enjoy them. That said I think they're quite rewarding when you get through them though.
Stalker trailer:
Mirror trailer:
Solaris trailer:
I'll throw out a few of my favorites. I'm gonna bend the rules a wee bit and mentioned a couple from the early 90s.
I know many posters here are big on war films, so I'll toss out what I think is one of the most brutal depictions of world war 2 portrayed from the Russian side and focusing on the atrocities the Nazis committed.
Come and See:
House - off the wall Japanese horror film. "Like an episode of Scooby Doo directed by Dario Argento." More goofy than scary, so much silly shit to laugh at.
Naked. Absolutely brutal and desolate, but also extremely sharp and funny. David Thewlis gives one of my favorite performances ever and the scene with Archie never fails to crack me up
Man Bites Dog. Brutal. Extremely violent. Funny as ****. This particular trailer is from 2019. I think the movie came out in 93 if I remember correctly.
Persona:
That's a few off the top of my head. Many more. I'll post some more when they come to mind, but for now I'm going to go back to looking for a free stream of Black Sabbath's Back to the Beginning.