I just finished watching pt.2 of the episode. I've seen this episode at least once before. But this was the first time in a long time. And I've gained a new appreciation for it.
I just finished reading an online review. The person who wrote it praised this episode. But he also took the time to point out the sorts of flaws that are inherent in most (if not all) older sci-fi TV shows and movies. With new technology things are obviously more realistic and spectacular. But in order to appreciate some of these older programs you need to ignore those sorts dated issues.
The power of this particular episode is in the message. And in the excellent way that the viewer is kept in suspense. It's well acted, too. With Robert Duvall. And with some other very familiar faces that are playing completely out of the characters they're better known for portraying. IMO, though, the actor Steve Ihnot is the most impressive. Not wanting to give anything away I'll just say that he plays his role perfectly.
I think this is a beautiful 2 pt. episode. And I believe at it's conclusion it will leave many people with a wonderful feeling. Something that I feel is terribly lacking in much of what I see on TV these days.