TOS-era Trek is an interesting anomaly to me.
When it's good- "City on the Edge of Forever" or "Balance of Terror" good, it can rank amongst the best science fiction, bar none. Good TOS gets scripts written by legends like Harlan Ellison and Richard Matheson.
And when it's bad- we get "Spock's Brain".
TOS doesn't really get to have a middle zone, and that becomes a problem for some viewers. They treat the whole series like it's nothing but rubber rug monsters and Shatner overacting and they miss the message the series sent.