A Psycholoanalization of Michael Corleone, via Star Wars

It was Michael's nature to be the more serious type. But I believe as he's got older, the transformation is evident. In GFI, he's this young kid, just finished his work with the marines, still has his life to live, his future's still up in the air. By the middle of part one, since his return from Sicily, his intentions are clear of taking over his father's line of work, and his joyful boyhood years have come to a close.

This same transformation of character is in Star Wars, Anakin to Darth Vader. First he's more human, and he has potential to be joyful, but he decides to pursue a job opportunity with the Dark Side and is more machine, both in a literal and figurative sense.

Near the end of Return of the Jedi Vader realizes what a monstrosity has occurred, and saves his son's life, also bringing an end to the head of the empire. In GFIII Michael comes to realize his previous actions, "killing my father's son", and feels like shit because of it. The thing is, instead of Vader converting one of Luke's half-siblings to the Dark Side, he dies in peace of the floor of a star destroyer. Michael doesn't realize what an evil thing has occurred and simply ends it, instead he hands the power over to Vincent.

Anyway, just my take.