I loved that show, but time has sure not been kind to the special effects. :)
I’ve noticed in some rebroadcasts from the original 16mm film that you can tell they had an eye to the show being presented on low quality TV. I’ve noticed the same with the old Twilight zone episodes.
You can see all sorts of flaws in backgrounds, sets, etc, that they just know would not be noticeable on a TV, but is glaringly obvious on a modern flat screen.
You can also see that Capt. Kirk used a stunt double to perform the fight scenes.
I have seen some old star treks with some new special effects put in, mainly on spaceship scenes.