I don’t really care for ambiguous endings, either, but neither do I like having everything spelled out for me. I like it when there is a definite answer to the puzzles, but I have to do some of the work of putting the clues together myself, as in Memento.
That said, I think there is a time for ambiguous endings. I don’t want to be told at the end of Total Recall whether everything was real or a hallucination.
In the case of “The Prisoner”, I don’t think McGoohan himself knew what was going on. It wasn’t possible to reveal what was really going on, because the people making the show didn’t know themselves, so they were left with coming up with an explanation that could never satisfy all of the mysteries posed, or the answer that we have, which really isn’t one.
SPOILERS FOR THE FINAL EPISODE OF THE PRISONER
My theory is that when Number 6 resigned, he was locked up, possibly drugged, by MI6 to prevent his revealing the vital information he has, and everything we see happening is an elaborate fantasy/hallucination that he uses as a psychological defense mechanism. When he sees his own face under the mask of Number 1, that is his own subconscious telling him that he did this to himself.
Or he was captured by “The Enemy” and what happens to him is an elaborate fantasy/hallucination he is employing to deal with the torture and drugs being used to extract the information, and his face on Number 1 is his subconscious.
Or he has gone insane, has no information to reveal, and the whole thing is an elaborate hallucination etc. The circumstances are really irrelevant to my theory; I think the key here is that it’s all in his mind.
Of course, the very problem is that the show supports any of these explanations and others that directly contradict them almost equally. One of the strengths of movies like Memento, Open Your Eyes and Blade Runner, is that, puzzling as they may seem at first, there is a definite explanation that is supported by the clues. You just have to know where to look.
No matter how much you look at the clues in “The Prisoner”, they don’t support any one explanation. This is one of two things about the show that bothers me, the other being Rover, which is just stupid. Unless you accept my theory above, in which case it does make a kind of sense.