I believe also that The Godfather Part III is the best throughout the trilogy. But, you see the thing is, its not much of a Mob movie.

Don't get me wrong, anything with The Godfather in front of it can be considered an essential Mafia item (minus The Godfather Returns), but its much more of a story of a man trying to redeem himself after a lifetime of sins. And with a subplot that involves such men as the Pope and other high ranking officials in the Italian government, it is definately one of my favorite movies period.

The only thing, that i can relate to that many see as a weakness in the Godfather III is that it is not set up like the other two movies. It is, indeed, a bit complex, and confusing on the first few viewings, but I find that, once you understand the movie in full, you can realize that it was essential to complete The Godfather legacy in its current state.