I remember being very puzzled by Kirk commanding the others to "set your phasers to 'Silicon', quick!" because it implied that that phaser beam was specifically targeting a single element which seemed strange, because in other episodes I had seen how people simply vanished if they had been hit by a phaser beam on full strength. Which makes no sense even if it was then set to carbon, because people consist of more than carbon alone: you would then expect all the hydrogen, oxygen, sulphur, nitrogen and whatever else is in there to remain behind.
Of course that would have been not a very nice thing to depict in a family-friendly show. But it seemed sloppy nonetheless (I'm not a geek girl for nothing), and that is why I have always remembered that episode.
I actually loved Star Trek, and I still like it. I liked the original series because they were so mysterious ... it was a re-run on the Dutch TV on Sunday somewhere in the mid-seventies, scheduled right after a German children's show called "Der Sendung mit der Maus" (The show with the mouse) (https://www.youtube.com/watch?v=GsBVW_zJU84).
Speaking about German TV, because we lived close to the German border we could also receive the German TV stations ARD, ZDF and WDR.
They also showed Star Trek at one time, allowing me to see even more episodes. Unfortunately, they had given it the dreaded voice-over treatment, as they always did with everything (except on WDR 3):
"Jim!"
"Ja, was ist den das, Spock?"
"Das ist ja ganz faszinierend. Ich bespüre ja unbekannte Lebensforme, aber ich sehe keinen richtigen sänkrechen Bio-Signatur."
- or, in Westerns -
"Jetzt klapp's mal los mit'm Pferde!"
"Yahoo!"
"Also nah du, Jack! Ich schiesse dich tot mit meinem Colt!"
They also used those strangely ill-fitting voices for the characters, and I also noticed that all female characters had the annoying habit of talking with way too much false air and a very nasal voice:
"Eleonora, liebling, kommst du mit?"
"*Aahhmm mmhuhmmja* Max *ahmuhmm mmmh*jah, was*hmmmuhm* sollte *hmmmumm* ich denn tragen?"
Re. Star Trek (again): there are some other TOS episodes that have always stuck in my memory. For instance, the one where they encounter those beings who vanish in a very weird way if they give up trying to get what they want (I forgot what that was though): it was as if they rotated away outside of the observable 3-D space ... as if they suddenly were just cardboard 2-D planes that turned along the Z axis so that they became a single line, that then contracted to a point and vanished.
See, how stimulating this is for a child to watch?

Another one I remember was about the Gods from the Greek pantheon who had, for some reason, taken up residence on a planet that the Enterprise stumbled upon, and naturally, Kirk got into some sort of conflict with them. I don't remember it for being very good, it was very campy in a way. I mostly remember that it all felt very unfair - just let those poor gods be, for heaven's sake. Or maybe they had some nefarious intent, but I don't remember it. I also remember that at the end, the Enterprise fired its phasers on some surface structure, which was seen from the planet's surface. The beams appeared as in perspective which I found very annoying: from that distance those twin beams should have appeared parallel. Sloppy.
Another one, that I found scary, featured Kirk and Spock (I think) manually putting some scary cobalt thermonuclear device (? - probably an early concept of a neutron bomb?) somewhere that was to be detonated immediately after they transported out.
Oh yes, and there was of course the one where they met a strange probe that called itself V'ger and that held the crew hostage by turning them all into a kind of cube-shaped biscuits. It could also accelerate time. In the end it turned out to be Voyager probe that had for some reason acquired intelligence but had part of its name erased.
Or maybe I'm mixing up some episodes now

The funny thing was that my mother absolutely loathed the show. I don't know why, but back then she had a bit of an aversion towards American popular culture - the phenomenon of "crooners" in particular. In that V'ger episode I remember her passing by the TV set, halting for a moment and looking at Kirk who was just having a verbal stand-off with V'ger, yelling at it "now listen here, you failed kitchen timer ... " with Spock standing by, looking worried.
She remarked: "how dreadfully ... American. Yuck."
I should ask her what triggered that feeling, because as far as I'm aware she doesn't feel like that now. Maybe her trips to Canada and the US have remedied it

I suppose she had an overdose of some sort of crooner music at some time.