Truly a great episode, and like another reviewer, when I saw this as a child in the 70s, I was absolutely terrified.
It's likely this is far too intense for 5 year olds even now. John Robinson's sudden turn from kind reasonable father/husband to barely controlled fury is alone extremely frightening, and that's just one aspect to it.
It's certainly true that Guy Williams' talent was criminally underused throughout the series. However, that's part of what makes this episode so effective. After watching a whole season of a kind father who's very slow to anger and never loses control, it's shocking because how well Williams plays it. And you also suddenly notice how physically imposing and powerful he is...
As a reviewer noted, the ending to Return of the Jedi is indeed quite similar to the ending here.
As an adult watching this, I couldn't help but laugh that the Robot somehow figured out that John was possessed. Quite a capable environmental robot!