TAS was my first Star Trek experience, I was only three or four so I don't remember a lot of details. I do remember, as others have said, that it was on late in the morning, so there was a little conflict over watching the show or going out to play. I think I decided in TAS's favor quite a bit. I only remember a few impressions of the show and can't sort most of it out from what I saw a few years later, when it ran in a weekday after-school slot. The main things I remember from the original run are the music, the ship moving "sideways" fast in the opening credits, and the rotating Scheimer-Prescott credit thing.
The next thing I remember were the toy commercials. My friends on the block had the communicator walkie-talkies, which worked OK but not great IIRC, and the bridge playset, the transporter part of which I found to be a disappointing gimmick compared to how it looked on the commercial. I got a 12-inch Captain Kirk figure sometime around '75 or '76. It went well with my Lone Ranger, Batman and Emergency!
Squad 51 figures, but soon Star Wars
hit and the 3-inch Kenner figures took over the play time of my brother and me.