It's particularly impressive to see how strong a character Barbara could be, how commanding and intelligent. We didn't see another female lead like that on the show for years after she left. The ones that followed -- Vicki, Dodo, Polly, Victoria -- were all pretty much just cute young damsels in distress who screamed a lot.
Christopher, I've got to disagree with you here and suggest you watch some of the surviving stories with Vicki. She was quite strong in some of them. And Polly certainly knew how to stand her ground with the old man.