I pretty much agree with everything in that article. The one big thing is complete games. It was always a big deal when someone came up or heard of a "cheese" or "easy way" to beat a boss or pass a level and have it still be there to use if needed. The pause trick in Mega Man 1. After shooting your electric shot, rapidly pause the game when it first hits an enemy/boss and the damage will tick every time you unpause the game. It made some boss encounters in that one a breeze.
Challenge I'm iffy on. Some games back then were flat out cheap as oppose to hard. I look at games like the Souls series, Elden Ring, Sifu and all of those have learning curves that once learned, make the game more manageable. Some retro games had the same formula, but due to the tech at the time, still ended up being really heap with respawning enemies if you move off screen then come back. Ninja Gaiden... Castlevania...
I've actually been on a retro style fix lately. Live A Live, Odin Sphere, TMNT, Mega Man, and some retro style current games like The Messenger. There's just something about that style of graphics that tickles my sweet-spot in just the right way.