I was totally thinking about The Prisoner as an example when this came up today! It's clear that McGoohan had gotten bored with neatly constructed thrillers, and wanted to create an allegory and explore deeper themes. The great thing about that show is that every individual episode was a neatly constructed thriller in its own right, even though it always ended back at ambiguous-square-zero (why is he in the village? will he escape or won't he?).
At the same time, it's pretty clear that he had no idea how to actually end the thing, and he told Lew Grade that shortly before they filmed the ending. I think the fiasco of the unsatisfying ending was only partly that people wanted an explanation which McGoohan didn't want to give them because it wasn't the point of the series. It's also that he kind of winged the ending and it just wasn't that good, compared to the high level of the previous episodes. So in a way it did fail the audience, even if at the same time the audience was failing to 'get' the art.
Edit: this is fun: https://www.youtube.com/watch?v=zfXqtDgvpL8
EDIT: Although, for those who haven’t seen the show, the video contains a massive spoiler.
Pardon my EDIT: The Prisoner, from 1967-8, was when ambiguity came to American TV, and with it Art (although there were precursors). To this day people argue about the plot of that one. People were so distressed at what they perceived, at the time, to be a lack of resolution (or their inability to deal with metaphor) that McGoohan had to go into hiding for a while. Really, the problem is that most people just don’t pay attention.