I had a boxed set of The Prisoner on DVD. It came with a documentary, made while the creator (head writer and star of the show, Patrick McGoohan) was still alive. Everyone they interviewed said he was a gentleman, that it was an honor to work with him, and that people didn’t understand the last few episodes of the show because he was misunderstood and ahead of his time.
Now I have a boxed set of The Prisoner on Blu-ray. That set came with a documentary made after Patrick McGoohan’s death. Many of the people interviewed say that he was a nightmare to work with, and that the last few episodes made no sense because he was making it up as he went, had written himself into a corner, and ended up having to turn in whatever ideas he had whether they made sense or not.
In this case the Blu-ray set makes more than just the picture and sound clearer.