I really did not like (whether it was Puzo's idea or not)that (spoiler) Vito got Tom's father killed, although I can see that the book needed this dramatic effect. However the story gave Vito's character a different angle(motivation), the position of Tom in the family changed (in my opinion it made his loyalty vulnerable. actually a lot of people knew about the murder, who could tell Tom BUT in my opinion to get to understand Tom we need his relationship with Vito& family to be very pure), it gave Sonny's character a different angle- all to the worse.