It would need combat that is fluid and challenging. And it would probably need lovely visuals that make it all a joy to look at. I don't know if perfection is a rational goal, but I can say that Unruly Heroes has come as close to platforming perfection as any game should be expected to and it'd be a mistake to miss it.
There are few RPGs I'd dare to call essential, but Divinity: Original Sin 2 stands out among all others as deserving of that accolade. It's undoubtedly one of the best tactical and role-playing experiences you'll ever have on any platform.
If you're looking for a standard Japanese shmup, Defenders of Ekron is going to disappoint, but this Chilean gem offers a nuanced level design that allows it to excel, becoming far better than most of its contemporaries through a revolving door of fun, challenging encounters and enough content to leave you more than content.