GURPS shifted my thoughts too; but for deriving a skill one didn’t have from one that one did.

V:tM was my first experience of a functional morality system.

Everway introduced me to not having hard rules for whether you succeeded or not.

My latest switch was Cthulhu Dark. For the idea that tests were about the speed one moved toward understanding the horror (so one could end up going either too slowly or too fast for comfort but always advanced).