I don't really care for TOS, I don't dislike it as a whole, there are some episodes I genuinely like but there are also elements of the show I don't like at all, I despise McCoy for example, I understand he's supposed to be the emotional one of the main trio but being emotional doesn't mean you have to act like a racist hick. I don't remember specific examples but too many times Spock made a suggestion that he explained logically and that really seemed to be the best way out of the situation they were in. McCoy's reaction can be summed up with "You emotionless, cold-blooded monster, you're worse than Hitler!". It was always personal with MCCoy, he attacked Spock, not his opinions, he ruins a lot of episodes for me.
I also don't think Star Trek was as smart as some fans (and apparently Roddenberry himself) seemed to believe, the crew of the Enterprise and human values were always shown to be right and "good", an alien society with alien behavior shows up? Expect them to be fixed by Kirk at the end of the episode. And the often cited allegories to 60s problems were so obvious and on the nose they make me groan, like the "Racism is stupid" episode with the black/white aliens.