So in the spirit of the thread: what game did you play that really made an impression on you and changed the way you looked at playing RPGs in general, or even the way you looked at your favorite game.
When I played DC Heroes for the first time, it was my first "point based" TTRPG (after playing D&D and Heroes Unlimited) and it BLEW MY YOUNG MIND. That degree of character customization was a paradigm shift for me.
Much more recently, I never "got" PbtA or FitD games until --after a couple threads here -- I gave Scum and Villainy a try and fell in love. But what really did it was a combination of watching Season 2 of Me, myself and Die where he plays Ironsworn, and then me playing Starforged. Complete mental shift on why people love that style of no/low prep, play to find out, narrative game.
Honorable mention: 2d20, for a specific element: I have adapted the Momentum and Threat pool to every game I run with a metacurrency. it works especially well for Bennies in Savage Worlds and Force Points in WEG Star Wars.