This is from a story here on CBR. I agree with most of their choices, but not all.

https://www.cbr.com/star-trek-origin...tial-episodes/

For fans of the original series, what are your 10 essential episodes?

Mine (in chronological order):

The Menagerie (season 1)
Balance of Terror (S1)
Space Seed (S1)
The City On The Edge of Forever (S1)
Amok Time (S2)
Mirror, Mirror (S2)
Journey To Babel (S2)
The Trouble With Tribbles (S2)
The Enterprise Incident (S3)
Spectre of the Gun (S3)