Some TOS episodes were based on classic scifi stories, like "Voyage of the Space Beagle". Also, Roddenberry employed established scifi authors like David Gerrold to script episodes.

An annoying facet of ST episodes is the morality lessons they push, like on every episode of The Brady Bunch.

For me, that’s the best part of the TOS era.

It’s nice to watch something that highlights the best of humanity in a future setting.

Almost everything else in SciFi is dystopian. But ST is a rarity. And it’s all the more beautiful for it.