If I could say any single game changed my life, it would be Secret of Mana. This was the game that kickstarted my love of RPGs in general, and probably the single best game on the SNES for my money. I still remember the day I got it, taking it home, switching it on and hearing this, the opening theme. At the time, aged 13, it was the most amazing piece of music I had ever heard in my life. Now... even now, it's still a front-runner.
Honestly, I don't have the words. See for yourself.