I'll state an old classic that is seen as a genre defining game because it is: Myst. Yes, it redefined the genre... in ways I fucking hated and that the adventure game genre took decades to fully recover from. It was a pompous mess in its presentation and was the worst kind of "doing action does vague thing or nothing at all, where is your hint book" puzzle gameplay wrapped in graphical hype which ages pretty poorly as far as appeal qualities go.
So many adventure games tried to be Myst afterward that the sheer budgetary costs and redundancy of the also-rans crashed the adventure game genre for years.
Super Mario World. Super Mario Bros 3 perfected 2D Mario platforming movement, then they added a cape that lets you skip most of SMW by flying at the top of the screen. Because of this, and because of other things that the cape makes too easy, speedrunners have created the "No Cape, No Starworld" category that features the parts of the game that would otherwise be skipped.
The spin jump is also BS, the fact that you can now jump on a bunch of things that should cause damage keeps me wishing that they stuck with SMB3 mechanics instead.
I think the cape and being able to skip levels with it goes right in line with the traditions of earlier mario games (1 and 3) introducing you to the warp zone by the second level. The ability to play the same game with ease or difficulty depending on your style is good design, I say. I do agree 3 is the pinnacle of the 2D era if not the franchise.
That's a take I really feel that I should have thought of saying first. I always did like SMB3 a lot more and didn't like most of the changes SMW made. Mario All Stars' remake of SMB3 was great for that reason.