I personally miss the science fiction / near-future vibe of Gen I, where it was implied that the PSS and revived fossils and a lot of the other features we take for granted today are relatively new inventions. It makes it feel exciting both in- and out-of-game. Not to mention the horrifying bioengineered weapon Mewtwo is emphasized to be.
It's not Pokemon exactly, bit the theme to Pokefloats captures the feeling I'm trying to describe pretty well.
https://m.youtube.com/watch?v=HS5OGrmE8j0 