Secret of Mana.
Used to watch my cousin play it. He had a big guidebook and everything, which I now have. I'd played other games like Mario, but this was something different. You had teammates to back you up. The characters talked (in speech windows), and often. There was an overarching storyline that was interesting. Your weapons and magic actually got stronger as you used them. You could use the money from your kills to get more stuff. And the music was nothing short of amazing.
Then I got to see the cast flying around the world. Holy ****.
I told him I wanted to play, so he gave me a file. I did ok on the fighting, even though I did it completely different from him. He set the AI to never attack, preferring to handle it himself. I set the AI to charge every opponent they saw, because I loved fighting things with an actual group, it was the closest I had to multiplayer those days. I wasn't so good on following the actual storyline though. 9 times out of 10, I'd go up to him after a cutscene and say "Well now what?"
It's still one of my favorite games.