A family is ship wrecked on an island.
Each episode began with, "IRWIN ALLEN'S PRODUCTION OF ... THE SWISS FAMILY ROBINSON". How many producers get the name before the title? And those titles and the series music cues were done by wonderful Richard LaSalle. LaSalle had worked on Irwin TV in the 1960s and it was these 1960s connections that made this series great....sometimes.
The series was great when some interesting pirates or Alfred Ryder dropped in on the island (this happened in about half the 20 episodes) but often just okay when it was just the family. There are exceptions to the rule such as the family focused episodes The Typhoon and The Treasure. The Treasure is classic Irwin Allen complete with an exploding volcano (again) and constantly shaking island.
William Welch returns from the bottom of the sea via the time tunnel to become series the story editor.
I think Irwin was playing a joke on viewers in the last episode The Devils. All 1960s Irwin TV shows began in a mildly realistic way and then went over the top with crazy story lines. Irwin seemed to be suggesting this with Swiss Family Robinson as well. In The Devils, something is seen moving through the dark, it appears to be a huge bat. Karl (the father) finds the garden destroyed and the livestock missing? Later, strange lights are seen in the sky. The Devil MAY have arrived on the island?
The series was enjoyed in my 1970s childhood so perhaps today I am looking at it through nostalgic eyes? I say this because many Irwin Allen fans of today just don't like The Swiss Family Robinson. I would say you need to have a love of Richard LaSalle music cues to really enjoy the series. His music in this series is so loud and ever present, the show would never have been the same without it.