Focusing on shows I liked as a kid but then went back to see and they weren't, rather than stuff that's just okay or I disliked from the beginning...
Speed Racer was like my number one top show when I was really young. I can't remember if I thought Speed was attractive, or I just liked the racer element. Regardless, I went back to it later and realized it was just terrible. I mostly liked Inspector Gadget for its opening song and its movie, but when I went back to see the show itself later, the sheer stupidity of the Inspector was just too much for me. Mighty Morphing Power Rangers was another top show for me growing up, I'd always come running inside to watch it when it was on and couldn't skip an episode, but....it's really not great. Better than any of its gritty or 'updated' remakes, though, even if it was super 90s, and all the rangers wore color-coded casual clothes.
When it was new, I was into Science Court, because I was a science nerd and I enjoyed the science + detective novel elements, even if I found it annoying that there was a designated 'hero lawyer' and a designated villain, and so the conclusion of every case was a foregone conclusion. Later I came back to it when I was trying to remember what it name even was and recoiled in horror from its artstyle. How did I ever even watch that??
Finally, I'm kind of scared to go back and watch any Magic School Bus, because I know I loved it, but how cringe and bad is it really? I don't remember. Maybe it's better I don't.