While my first Fallout game was Fallout 3, I never get far enough to get across a supermutant back then. My computer wasn't powerful enough, it overheated after the first half an hour of playing, the gameplay seemed rather slow for the "I WANT COOL THINGS" kid I was, so I never continued playing. My main interest in playing Fallout back then was to become a mutant (didn't read a lot about it, I just figured it was post-nuclear, there was radiated shit to eat, so it MUST allow me to become a mutant if I eat enough of it!).
Later, being a bit more mature and having passed the stage where there is nothing funnier than random killing of pedestrians in GTA, I played Fallout 2. I figured I had managed well enough with my tactics and my character creation and my quest solving to go and beat those nasty mutants in the Mariposa base! I was successful at killing the one eating rats in the first level, and the one at the entrance of NCR, so what could have gone wrong? A flamethrower, that's what could go wrong. I didn't even make it far enough to run for my life, I didn't last a turn. I still remember my PC running, set to flames, screaming for mercy. That was my first experience at how powerful supermutants can be.