First of all, the story ended with part III. Sadly enough after the brilliant first two parts, FFC & Puzo made a 'redemption quest' of the cruel Michael Corleone. They punish him though, in the end, with the ultimate sacrifice: the death of his daughter.

Where it had to end with him killing his own brother, they stretched the torture of Mike a bit. But when Mary died, Mike died. That's it.

Second of all, I think it's a disastrous idea to show us the 'happy years'. Not only was the whole saga affected by PART III, but the brilliant first movie (the Brando movie) would be affected as well if one of it's strong characteristics (the assumably notorious past of top crime boss Vito "could I have gotten to him ten years ago?" Corleone) is damaged by showing it all to us.

The Godfather is NOT a story about a succesfull crime syndicate. It is about what happened to a Family, long after it's destiny turned out to be crime and murder and such. We have seen what happened to the father, the mother, the sons, the daughter and the granddaughter. What more is there left to show? Vincent? Young Vito again? The Godfather is about family, not about mafia, I think.

I really love all three movies. I would definitely see a part IV, for the sake of it. But please, Paramount, DON'T! It just can not work anymore...