In my mind, Bobby D is one of the best mob actors in cinema history. It was hard to figure out which role he was good in and bad, but here are my final decisions:
Good:The Godfather Pt. II(His first big film and he gets an oscar? Not many actors are lucky enough to achieve that.)
Bad:Flawless(DeNiro looks like a gimp hanging around with a clown in a dress.)

It's not personal, it's strictly business-Al Pacino/Godfather 1