I bought the boxset the day it came out, at what was (and still probably is) a very good price. I don't remember exactly what I paid, but I do remember it being the lowest price in any of the stores I checked by far.
I happened to rewatch them a couple weeks ago (before this thread), and I really don't see anything terribly wrong with them. I remarked to my roommate that it's one of a dwindling number of DVDs where the image actually looks like film instead of video.
The movies aren't supposed to be bright and vibrant and overly sharp. The DVDs seem an accurate representation to me of what the film is supposed to look like. Francis Ford Coppola contributed full-length commentaries for the entire set, and he seemed pleased with the transfer. Yeah, there were a couple scenes that might have been a little overly dark, but every time I thought so, immediately FFC on the commentary mentioned that was how it was shot, or he felt when he shot it that he went to far with this look or that - in other words, if there any faults with the contrast or brightness levels, those are faults with the original movie and how it was made.
The only way I could be remotely persuaded to rebuy The Godfather I & II on DVD again would be if FFC recorded all-new commentaries, as he is an incredibly engaging speaker. But if FFC's going to be recording anything, I'd rather it be for Apocalypse Now - now there's a film that could use a reissue, with both the original and redux version included, the 'Hearts Of Darkness' documentary, and a new commentary.
The Godfather, as is, works just fine for me.