As someone who knows very little about technical matters... After re-watching some games shown on the PS5 presentation I think the aspect people are underestimating about the 9th generation... Is realism. But not in a purely visual sense like in "wow, this person and this landscape look so real", but more like... How things behave in our world.
This generation, save for some select games that go far beyond your average title like Red Dead Redemption 2 or Breath of the Wild... Both the characters and the enviroments are pretty much static. An explosion occurs. Yeah, maybe one or two predefined assets will catch fire like barrels, cars, etc. Or burst into pieces that will disappear after a few seconds. But that wooden house next to the explosion? Intact. The ground? Not even a stain of black. People and animals? In some games you'll be lucky if they even acknowledge that the explosion occured at all.
Now, look at Ratchet & Clank and the new Oddworld. These games are not even open world games. Yet the amount of shit that breaks, explodes, burst into thousands of pieces and overall reacts to our actions and the actions of the enemies/enviroment is insane compared to the average gen 8 games. Not to mention that they do that while boosting both resolution and overall graphics to levels that would be impossible to achieve on last gen machines.
And these are only the first games, and not even truly big ones. Imagine what they will do two, four or six years from now. We might see games were things that we take for granted in the real world but percieve as "unreal" in games due to the usual limitations of hardware... might actually be possible.
I think truly interactive games (or at the very least MUCH MORE interactive) will be the true advance this generation. NPCs that react more, enviroments that can be affected by our actions, objects that will behave more realistically...
Or maybe I'm just talking nonesense. Who knows xD