Worst show I've ever seen was Horse Land. Unfortunately, it was so awful that it crossed the line and became one of those cartoons that's actually hilarious if only because it's so bad.
I've only ever seen one episode but it's one of my favourite things ever and I love making friends watch it with me. It's about a horse ranch and some of the kids who live and/or go there. Each one has a ridiculously coloured horse (streaked manes, that sort of thing) that matches their eyes or clothes. The animals (except one horse, as far as we could tell!) can all talk when humans aren't around. The sheep dog (named Shep) is voiced by a Sean Connery sound-alike and there's this cat who is over-dramatic about
everything and tries to ruin everything for all the animals. Also when Shep isn't being Sean Connery because he is in the presence of humans, he has ONE BARK. They seriously sampled just the one bark and use it
repeatedly the whole time so it sounds just ridiculously fake. The animation is terrible at best and to top it all off, every so often the voice actors sound all righteous and they get louder and all of a sudden, with no build-up at all, they give moral lessons so kids will clue in, I guess? But then at the end of the episode they all sit around and literally say "Well, I guess the moral of the story is..." so why even 'hint' at it in the first place? It was just so awful I couldn't help but laugh at everything.
Link to the episode is here. :P
But uhh... as for cartoons that were bad with no redeeming features, probably the early-childhood stuff around today. :/ Any show that attempts lazy interactivity like Dora the Explorer and all that just makes me feel so bad for today's kids. Not only do I doubt how educational that stuff really is, but it just looks so boring! I would hate to be a kid these days. :( What was wrong with Magic School Bus as a teaching tool!?
Also Family Guy and its spin/rip-offs are pretty bad nowadays.
