From the interviews and histories that I've read/watched, the EAD[0] dev team was doing some of the highest level UI design in the world in the 80s and 90s.

They started each game from the interactive experience and then fleshed out the details from there. Think running and jumping in Mario - they spent months getting the gravity and speed right, the button presses, all before the first thoughts to art, level design or story.

It was very iterative. They'd start with a concept and then tweak and tweak and tweak until it was as fun as they could get it.

Another good example is the development story of Super Mario Kart[1], which was supposed to be the sequel to F-Zero[2], but they invented/discovered new gameplay elements that fit better with the Mario brand and they took the game in that direction.

[0]https://en.wikipedia.org/wiki/Nintendo_Entertainment_Analysi... [1]https://en.wikipedia.org/wiki/Super_Mario_Kart [2]https://en.wikipedia.org/wiki/F-Zero_(video_game)