These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Narm Charm: Leonard Nimoy riding high on his success in Star Trek, rocking the 70's 'stache, delivering a completely serious and compelling narration of mysteries ranging from the topical, to the unheard of, to the completely ridiculous. And it is wonderful to watch.
Nightmare Fuel: The series had a music score that when combined with Nimoy's voice was enough to guarantee nightmares, especially when the episode is about nightmares.
The screaming skull.
The profile on Carlos the Jackal, to a child in the 1970s watching this show that dealt with ghosts, monsters and the like, the inclusion of this real life cold blooded killer terrorist felt terrifying as a real threat, only mitigated slightly by the footage at the end of commandoes training to fight him.
The loving description of a theoretical 1906-level earthquake in modern Los Angeles in the "Earthquakes" episode.