Having exploration and post-game being relevant (for the latter, something like Kanto in the Johto games, the Sevii Islands, or the Battle Zone; as for the former, Sinnoh did it best imho), cutscenes which can be skipped, and a good mix of older and newer Pokémon (RSE is my model here, but DPPt also did that well, as the older ones were nearly equally from all previous generations, and new Pokémon still stood out).
And honestly I don't really care much about the story, still I would even strongly prefer a nearly plot-less Gen I/II kind of thing rather than having once again a plot that can be summarized in "evil team wants a legendary in order to rule the world".