To get a more realistic appraisal you need to hear from someone or was in their teenage years or twenties in 1966.
I started watching TOS in 1969 or '70 when the syndicated reruns had already begun. I was 11 at the time. "The Man Trap" was not the first episode I saw so I had no thought the series would be monster of the week. I can't really recall which was the first episode I saw other than I think it was either "Charlie X" or "Balance Of Terror," but I'm not really sure.