Crystalis on NES.

I had the game when I was about 6. Before that point, I thought of Nintendo games as something you played for an hour or two, then just turned them off. I thought Crystalis was a game where you kill stuff with a sword, and never considered there might be an ongoing story.

I remember one day brushing my teeth and thinking "I wonder if that flute in the item shop that says it wakes people up would do something to the guy sleeping in the cave..."

I put the game in and tried it, and opened up a door to the next level. It blew my mind. After that I was an RPG addict. I like to think it opened up my mind to puzzle solving and higher level critical thinking skills.