One of many: the laser-sharp focus of an arcade game merged with a more modern 3D action game's mechanics, while also adapting some of the strengths of a modern game's structure. A basic example could be made out of the Platinum action game template.
So you'd start up this game and after a brief scene-setting intro you'd be playing through what is basically an arcade campaign. A series of Platinum-style battles, complete with bosses, but crazy-dense and with a ton of different enemy types and frequent environmental changes. Minimal cutscenes (again, like those little snippets in an arcade game). Around 30 minutes long, but tough enough to have you undoubtedly fail at the start and have to retry the whole thing and learn a bit before you're capable of clearing it.
But then, when you do finally clear it, instead of getting credits you find that you get to explore at peace for a little bit. Maybe you gain access to a very select few new abilities. And then you find maybe two new "dungeons" you can take on, each of which serve as what is essentially entirely new arcade game campaigns (so again, 30-40 minutes long, lose a life or two and you restart the whole thing, tons of variety, extremely dense), only they're a little bit harder and longer than the first and they're tailored to these select few new abilities.
And this repeats. This could give you the grand sense of adventure of a modern game structure, but with the intensity and concrete sense of raw skill-based progression involved in clearing an arcade game at the core (only in a progressively more intense loop). The idea of every "dungeon" being some kind of Capcom belt-scrolling masterpiece viewed through a modern Platinum lense would be a massive undertaking, but that's what this thread is for!