I remember reading somewhere (Lebo?) that some Paramount big-wig told FFC before GF II was released that "You have two movies here, and neither one works. Get rid of one of them."

That said, however, I think that the flashback scenes were brilliant in their execution, particularly with respect to their costumes and sets, although except for DeNiro's brilliant portrayal of the young Vito and Gaston Moschin's Fanucci, there isn't very much n the way of acting.

Had they been eliminated and the contemporary story expanded I don't think they would have been missed, however their inclusion, particularly in the way in which FFC used some of them as a counterpoint to the main story added to its overall quality of the film and helped greatly in making it a masterpiece, rather than simply a sequel which might not have stood up against the original.