Ooooh, that's a tough one because there is more than one game, but... those two games will be my forever loves:

This is hands down my favorite Final Fantasy game ever! The characters are still some of my absolute faves, the sidequests and Easter Eggs still make my cry and the game mechanics are SO FRIGGIN EPIC

And then: Skies of Arcadia. Starts out as your run-of-the-mill "gather some crystals to save the world" plot and then it disolves into unexpected PLOTTWISTS! Genius.