I guess I'm a bit of a late entry regarding this thread.
I purchased the DVD set of the first 2 seasons of the ADVENTURES OF SUPERMAN when they were first released. I didn't purchase the later color sets as I felt, with a few exceptions, that the storylines weren't as strong and somewhat "childish".
With regards to the visual quality of this set, I felt it was only fair, with some episodes being marginally better than others. Many fans of this series were hoping for prints made from the 35mm masters. Instead we got 16mm dupe prints which were contained on Beta Tape made just prior to the shows debut on Nick at Night in the early 1990's.
Warner Brothers is generally known as a penny pinching organization and I believe they failed to do a thorough customer research survey prior to the DVD release. This left them being unsure as to how popular this DVD set would be. IMHO those in charge of putting this DVD set together were either too young to remember this series or just didn't care and were looking to make a fast buck. In talking with some people in the know, most of the 35MM masters do exist...some in better condition than others, but none that are too far gone to restore. Personally, i would have paid more for this set if more restoration work had been done.
On a sidenote, the commentary by Noel Neill and Jack Larson on the DVD set was done by them for free. Warner Brothers refused to pay them and so they did it for their love of the show and for their fans. Noel and Jack told me this in person.