If you're referring to series then among the best Seinen classics are shows like:
Berzerk (1997)
Monster (2004) [My personal favorite]
Cowboy Bebop
Steins:Gate
Vinland Saga (newer)
Frieren (newer)
There's a lot of Shounen classics as well, my favorite probably being
Full Metal Alchemist: Brotherhood
granted there's several tropes in it that aren't going to be as enjoyable to watch on repeat for older folks. But the storytelling and plot is practically like Breaking Bad but in anime form.
EVA should not be missed, regardless of how weird and gross it can be for some. I watched it for the first time a year ago after hearing so much about it.
The first five or six episodes are an awful slog, and then there's an exponential curve up through 'quite good' into 'great' then 'I understand why this will print money forever'.
If you're sold but confused how to watch: start with the original release and then watch End of Evangelion; both on netflix.
Paprika is good, but I wouldn't elevate it to greatness. Whereas, for me, Perfect Blue makes the cut. The odd thing is, they both essentially explore aspects of the same theme: subjective reality and what happens when those of different individuals' collide. But they do that in very different ways...
And thank you for bringing up Metropolis, that film tends to be underrated.
Your Name
Violet Evergarden
Perfect Blue
Paprika
Metropolis
There's a bunch of great animated movies.
If you're referring to series then among the best Seinen classics are shows like:
Berzerk (1997)
Monster (2004) [My personal favorite]
Cowboy Bebop
Steins:Gate
Vinland Saga (newer)
Frieren (newer)
There's a lot of Shounen classics as well, my favorite probably being
Full Metal Alchemist: Brotherhood
granted there's several tropes in it that aren't going to be as enjoyable to watch on repeat for older folks. But the storytelling and plot is practically like Breaking Bad but in anime form.