This is like having to pick a favorite child...

For significance in shaping the types of games I would be drawn to for the rest of my life: Final Fantasy on NES.

Played almost all FF titles released in the US after that. It made me love all things swords and sorcery, so I am also a major fan of the Elder Scrolls series, the Witcher series, the Dragon Age series, and the Baldur's Gate series, among many others.