Lost in Space. In the first season they tried to make it serious SF (but not very hard SF; in the first episode, the ship was damaged by the heat from a comet
). Then somebody heard the Call of the Camp, and we were seeing space pirates and space cowboys and giant talking carrots, and Dr. Smith morphed from a scary villain into a cowardly butt monkey. "Oh, the pain! Oh, the pain!" Which do you think was better?