This is a rather good commentary. It is led by historian and consultant Scott Michael Bosco asking questions to director Jeannot Szwarc. The conversations flows nicely throughout the movie and they give a lot of information, mostly on technical aspects of the filming.
Bosoc, who was a consultant on the production of the dvd, as well as in the release of the Director's Cut, leads the conversation asking pertinent questions, which shows a very well prepared and researched commentary. There isn't a lot to this commentary just as there isn't much the film itself but it does add to the experience of viewing Supergirl in terms of context and the pretenses of the film. They talk on lenght about the effect the editing had on the final product (specially the highly edited US version), affecting Slater's performance as well as the depth of the story.

Good commentary altogether, perhaps strictly for fans of the movie though. No real filmaking insight here.