I know I am in the minority here, but I did not like the entire flashback scenes. I felt that some of them were quite slow moving and did not advance the story as much as one would have expected for the screen time given to those scenes. However, michael's story was very strong. It was a continuation of the part 1 and showed the scale of his buisness and the fall on the personal front.
Part 1 offered great scope for each of the roles and development of each character and an inspiring story to begin with.
Both were great movies and occupy the top 2 slots in favorites list. However, if I can watch part2 a 100 times, I can watch part1 101 times.