The worst and most boring stuff I ever saw:
- Dragonball (Z/GT): Repetitive, slow, etc. Like a lot of people already mentioned before me. I did like the planet-travelling stuff at the start of GT though...
- Pokemon: Repetitive with a capital R. Every episode it's "Pikachu this, Pikachu that". ':| And not to mention that Team Rocket was there EVERY EPISODE except for the very first one where Ash got his Pikachu. Blergh.
- The Melancholy of Haruhi Suzumiya (boring, but not bad): I love the plot... But some episodes are mere fillers with some bring ones among them (The Boredom of Haruhi Suzumiya was the worst). I liked it when I watched it, but yeah... The non-chronological order of watching is confusing, and if you watch it chonologically stuff is going downwards after the first 6 episodes. The chonological ending is very lame and you don't know what exactly happens even though you watch the series in the chronological order.
I loved the twists of cliche's, but that's all that there is to this anime.
I never watched Naruto (except for one episode a friend showed). So I can't rant about that series.
Digimon season 1 and 2 where awesome. But I never watched stuff beyond that.