I've been thinking about this some more and I think the reason GF I and the young Vito story in GF II are what really hooks me into those movies are because the events that take place are on a smaller local level. Even though I enjoyed all three, the story of Michael moving to Nevada and getting into bigger broader things which leads into GF III on an international level are all things I will never experience in my lifetime.

But the little things in GF I and Vito's story in GF II are very tangible in our everyday lives. They are something that if we were in the right place at the right time we could get caught up in ourselves. The whole taking over of major corporations and the involvement of God's Mafia, the catholic church, becomes too big to relate to.