I know he had to die at the end of GF I as a matter of the plot, but I kind of wish we could've seen him interacting directly with Michael--How Michael might've contended with Barzini; Who was the smarter man, the better "chess" player. Barzini seems to have been just as respected as Vito and about equal in intelligence, but with more of a modern edge to him. I just wonder how the two would've dealt with and contended with each other. In general, I wish Barzini would've gotten more screen time.

I would've liked to have seen just what the other Dons--Barzini, Tattaglia, Cuneo,and Stracci were like in comparison to Vito and Michael; How they came up and how they ran their families--If any of them were "Godfathers" in their own right, or if they ran a colder and more business oriented ship like Michael later did.

In any case, I think Puzo created enough compelling side characters that I would've loved seeing a spin off dealing with the other 4 Heads of the Families prior to and after the events of the first Godfather.