these are the ones I played. (Ranges from serious to stupid)

FF4: Redemption
ff4: The first one with a brooding main character.

FF5: Another Warriors of light game with the job system.

FF6: Destiny

FF7: Memories of Life

FF8: More angst and traces of a plot

FF9: Revival

FF10: Spiral of Death

FFT: Dark Ages

FF12: I can't believe it's not star wars!