"The Hidden Thing" did have potential to be good. Robert Stevens was the most prolific director of 'Alfred Hitchcock Presents' and was responsible for some truly fine episodes, including in Season 1. This is not the first appearances on the series for Biff McGuire and Robert H. Harris, they were in previous episodes and both were watchable. The idea for the story was intriguing even if not original. While the series had its weak points, when it hit particularly high it was brilliant.
Brilliant "The Hidden Thing" turned out not to be by any stretch of the imagination. Really did want to go against the grain, considering its potential, and say that it is not as bad as others are saying, but to me it is that bad. It is a strong contender for the worst episode of Season 1, and none of the things the episode was seen for come off well. Considering the potential, "The Hidden Thing" really should have been so much better and everybody involved deserved much better than this. And no, this actually is not a case of one aspect completely ruining things.
It is not a complete disaster. Harris has enough pretty good moments and gives the only halfway decent performance of the episode, the reaction to being called a nut is indeed priceless. Hitchcock's bookending always entertain, and it is amusingly written and nicely staged here.
Also thought that the episode doesn't look too bad, though there are better looking episodes of the series, and the main theme for the series is deservedly iconic.
Unfortunately, that is it when it comes to the praise for "The Hidden Thing". Am another person that thought that the acting was not good, especially at the beginning. McGuire does not look at ease here and there are no fireworks in the chemistry throughout. Stevens' direction is uninvolving and lifeless, had a hard time believing that it was Stevens directing. The dialogue tends to be clunky.
Story-wise, "The Hidden Thing" is pretty much a mess. It is thin, while also trying to rush through the second half, and lacks any kind of suspense. Also found it pretty silly too when it increasingly lost credibility later. The characters are mere ciphers with motivations that are vague at best and not delved to anywhere near enough, so actions made no sense and made the characters look stupid. The worst thing about the episode is the ending, while not single-handedly ruining it it brings it down considerably. Calling it a head-scratcher is being far too kind.
Overall, weak. 3/10.