Tetris never really goes out of style tbf. There's something too fundamental about it. Pong was the first truly timeless game imo, one of the very few of the arcade generation. People could still play a basic version of that and enjoy it 100 years from now, it'll have some appeal. Tetris is the best example in that camp. It's a masterpiece. It requires no nostalgia to appreciate, no real background or anything. Just a really simple, dopamine-escalating puzzle that is accessible to pretty much all. SMB3, Chrono Trigger or Ocarina of Time can't say that, they all require you to be the sort of person that enjoys that sort of thing. Tetris really doesn't, you could give it to someone that hates video games. Just mute the volume maybe.
It'll outlive us all, in similar iterations to its current form. Most powerful thing to ever come out of Russia, hands down. Putting a man in orbit? Whatever. Fields full of tanks and a huge nuclear arsenal? Meh, fat lot of good its doing them. Atilla the Hun? Okay, could make a case there. Tetris, though... The west has never truly matched it. I think Candy Crush is the closest we've gotten.
Not really you. The difficulty was naturally higher, for a wide array of reasons, most of which get ignored. Inputs were poorer, the management of difficulty curves was basically lolrandom, people didn't know how to really tutorialize yet, etc etc.
Tetris doesn't really suffer from any of these. Either they got lucky or designed it very smartly. Prob both. It's a masterpiece. Most retro games aren't, even our favorites.