The Godfather Trilogy is, as a whole, the best achievement in filmmaking that's ever happened.
Brilliant stories, brilliant performances (Marlon Brando, Al Pacino, Diane Keaton, Robert Duvall and Robert De Niro stand out as excellent leads) and top class cinematography coupled with great scripts make Part I and Part II so compelling to watch.
The same should be said for Part III. I don't know why people criticise it so much. Granted it's not as good as the other two, and the casting of Coppola's daughter as Mary Corleone was a stupid mistake, but as a whole I think the film is excellent, especially the climactic finale. So why people hate it so much is a mystery to me too.
As for the DVD, well the picture is vastly improved. Having seen most variations of the VHS versions, I can say that they've worked hard to improve the picture and sound for the films.
The extras are amazing. With many lengthy featurettes, well over an hour's worth of deleted scenes for the first two films (and an alternate beginning for Part III) plus more, it'll take ages to watch fully.
So, let's see - 9 hours of the best film saga ever, with a whole host of extras - this is a DVD you can't refuse.