I remember when the series first played in the US. We had just gone through the "Battle of Chicago" and were about to begin the slow slide into mediocrity with the election of Richard Nixon. We were a year after the "summer of love" and a year before "Woodstock Nation". Drugs were still a new phenomenon in the American middle class, and enough of us believed that there was still hope to galvanize a huge portion of the population. And then, in the middle of it all, came the face of a smiling No. 2....
The Prisoner is truly an archetypal series. It so accurately reflects its time in both its excellences and its deficiencies. There's no question that the majority of the episodes play better to a cannabinolized audience; and I won't argue with someone seeing the series in the 21st century for the first time who complains that there are so many plot holes and bad acting in so many of the episodes that they can't understand why anyone would consider this worthwhile.
But then, there's "Once upon a Time".
This is more than an episode. It's more than a TV show. It is high drama and classic stagecraft. When seen without commercials, it has the impact of a Beckett or Pinter one-act. It is unquestionably McGoohan's magnum opus. I expect that someday, perhaps in the not too distant future, someone will get the idea of putting it onstage, along with "The Dumb Waiter" or "Play", so that the author will get the recognition he deserves as a playwright. But in the meantime, if you have any affection for "theatre of the absurd" or "comedy of menace", you should make this episode a must see. And if you've started the series but have lost your enthusiasm after an episode or two, skip right to this. Once you understand the premise, you don't need all of the prior 15 episodes to fully immerse yourself in what cannot be denied is an exemplar of 20th century dramaturgy.