So many opinions be touted around as if they're fact.
To me TOS may well have laid down the foundation, but greater things were built upon it. Of course it hasn't aged well. Heck we have more modern technology today than when TNG, DS9 and VOY were airing. It happens and perceptions of the futures change accordingly with time. Besides, a lot of novel writers would be out of work if they couldn't recon mistakes in the shows/movies.
Shatner and Nimoy never seemed more than average actors to me. Certainly the characters they played were iconic, but their acting careers beyond Star Trek weren't that great in my opinion. Don't get me wrong, TOS has a number of great, well written episodes, but it also has a number of just... faceplaming ones. Over all the pace of the show is just too slow to keep my attention or more accurately, my interest, for any amount of time.
It really was the TOS movies that really got me liking the characters more so than the show. Which is why I have to ask if you're talking about the show or movies when asked which series I like better. Certainly there's something to the even/odd rules concerning which movies are better, but for the most part they told a single story, had great adventures and it was fun without being slow or repetitive like the show can be.
So that's my opinion, take it as you will.