I've seen parts of GFIII and once even got through about the first 40 minutes before I had to change the channel just to stay awake. But you are partially correct, I've never seen the entire film straight through.
However the numerous parts I have seen, plus the infinite discussion about it here on the BB Board, plus the fact that many of those who DO happen to like it have made it clear that they don't consider it equal to the quality of the previous two....THAT is what makes it impossible for me to fathom how anyone can consider it the BEST of the Trilogy. The simple miscasting of both S. Coppola and G. Hamilton already bring it down a level from the almost perfect casting of the others.
Another mystery is how anyone can consider Pacino's cardboard cutout performance in GFIII to be better than those of the first two. I agree his silent scream at the end is one of the finest acting moments in cinema history; but overall, his portrayal of Michael Corleone in GF and GFII are far superior to that of GFIII.
AppleOnYa