The only interesting arc that DBZ had was the Cell saga. Keep in mind, though it did contradict the earlier statement of the Super Saiya-jin being the greatest power in the world as well as the fact that Goku didn't have the monopoly on SSJ, Cell was actually an interesting villain. Unlike any of Goku's other opponents, Cell was a very cunning and underhanded fighter. And before he absorbed #17 and #18, he actually dealt with the Z Senshi with common sense and intelligence. Instead of fighting them in his imperfect condition, he chose to liquidate towns and villages so that he could boost his power level from all the humans he absorbed. And he always used hit-and-run tactics so that they could never trace his ki and he was always on the move. Cell only got retarded because he felt that he was "Perfect" and his Saiya-jin heritage was making him way too arrogant. Imagine if Cell had instilled a reign of terror somewhat similar to his predecessor Demon Lord Piccolo? Instead of having the Cell Games, imagine if Cell framed the atrocities that he committed on the anthropomorphic animal people as well as the Z-Senshi. Regular humans would start to accuse their fellow neighbors and friends for being associated with that "freak" Cell. And imagine the shit hitting the fan if Cell were to reveal on live television that he's technically a clone from Son Goku's cells? The former hero that defeated Demon Lord Piccolo is the one who spawned Cell? It would be worse than any sort of genocidal destruction that Cell could pull. Not only is Cell far more powerful than the Z Fighters in his Perfect stage, even if he loses, Goku and friends have lost the trust of the people they're tying to protect.