The only TOS-R episode I have is Enterprise Incident
(which is one of my faves) simply because it visually makes more sense
. I can live with the 60s fx for the other ones. But maybe I'm missing something.
Well, it's more to do with the technical aspects of things. The special effects were very low resolution compared to the film stock, so when they cleaned and prepped the series for HD, the special effects had to be reshot. In the process, CBS Digital decided to update them for a more modern audience.