The TOS movies were (for the most part) genuinely theatrical experiences. The TNG movies were (for the most part) genuinely not.
See, this "TNG movies are just two-part episodes on the big screen" thing is a hard thing to shake. Even the lauded First Contact suffers to some degree. I can't help feeling it was the mentality of the production team. TOS movies were made by 'movie people', and even when TNG was off and running from 1987 onwards, the TOS movies were still
their own beast, entirely seperate from the television production pack. There was a line in the sand between the two iterations of Trek. However, starting in 1994, Rick Berman was put in charge of both
movies and television, and I wonder if he brought a television sensibility (the "sausage factory" approach to working out a story) to the movie series. The way the scripts were structured, the way they were shot, it was a completely different world because the people behind the scenes were coming from a completely different school of thought to the 'movie people' who had helmed Treks I-VI. One can't help wonder if it might have been better to have had TNG move to the big screen, but still maintain a seperate production team rather than trying to amalgamate everything 'Star Trek' under one banner.