It’s probably not controversial to say that the Dungeons & Dragons game from 1974 was the most important and influential game in the whole genealogy of all RPGs. Every game that followed was either an attempt to make a game that improves on D&D or make a game that is different from D&D. They were either a direct response to D&D, or expanded on a game system that was.
The real question is, what other games can be considered hugely influential on how people design game systems today?
In my very own opinion the RPGs can be crudely divided into 5 or six generations or stages (with a lot of overlap and finicky stuff) depending on some “development” or “evolution” in rules sets and gaming styles.
… ehe, slightly more than two cents of opinions …