What is so special about WB Game's "Nemesis System"?

I never played the games said mechanic was in, so bare with me as I only seen a YT Short going over it. Something about sparing or killing enemies will reflect how they interact with you later? I don't see why that specifically needs to have a copyright pattent on it for another decade. RPGs like Fallout and Avowed already do something like that where your actions will dictate how enemy factions will treat you.

So, what is the the detail that makes the Nemesis System stand out over the rest?