I think the worst part about TNG is that they never revisited some of the former planets TOS went to, precisely to see what happened to them and perhaps show a different pov on the necessity of the actions taken by TOS. Piece of the Action, etc would have been most interesting.
They also dropped the Preservers/parallel development angle entirely, which could have been good. And instead of aliens using the Paramount period wardrobe (Romans, Nazis, etc) they went to the forehead widget. Ah well.
Star Trek Unlimited #10 Jul 1998 (A piece of reaction) showed just why the show didn't go back to worlds Kirk had visited--it made the TNG Federation look more idiotic than in Kirk's time.
"Think we should at least check up on that planet Kirk messed with over the next 100 years?"
"Nah, what is the worse that can happen?"
For the story have any meaning the Federation would have not done any follow up since Kirk's time and that was ridiculous.