Spoiler warning for all DBZ sagas
Originally inspired by the eight beads in the Japanese epic novel Hakken-Den, the seven Dragon Balls were a fascinating story element in Dragon Ball Z Kai. While these magical spheres are prized for their ability to grant the user whatever they desire (to an extent, at least), the Dragon Balls were often used to resurrect the dead - most notably when Goku and his friends fell in battle.
By the end of the series, however, it could be argued that the use of the Dragon Balls had reached its creative limits. From the first episode to its last, the Dragon Balls were used more like a Phoenix Down from Final Fantasy, than a genie in a magic lamp capable of doing the impossible.
So, how were the Dragon Balls used in Dragon Ball Z Kai? First, Goku was brought back to life with the Dragon Balls after he was killed by Raditz in the Vegeta Saga. Then, the Dragon Balls were used to bring various characters such as Krillin and Piccolo along with the majority of slain Namekians in the Frieza Saga back to life. Following that, all the innocent civilians killed by Cell in the Cell Saga were resurrected, including Android 17 and his twin sister Android 18. Finally, all the main, side, and minor characters killed in the Buu Sage were once again brought back to the land of the living.
With all these constant resurrections taking place in each saga, the likelihood of anyone staying dead in Dragon Ball Z Kai was zilch. With the Dragon Balls acting as a reset button, the dramatic tension the series once had was gone.
Before Dragon Ball Z Kai, the Dragon Balls were used in different ways. In Dragon Ball, we saw the Dragon Balls grant Oolong a pair of panties and restore the demon King Piccolo his youth. There were also characters who brought back from the dead, such as the Indian Bora, but it never came close to being excessive as Dragon Ball Z Kai. The concept of the Black Star Dragon Balls in Dragon Ball GT was interesting - after a user made a wish, the balls would be scattered across the universe and would need to be returned to the planet the wish was made on to stop that planet from exploding one year later. But unfortunately the concept suffered in execution.
Perhaps the most interesting thing Dragon Ball Z Kai did with the Dragon Balls was introduced the Namekian versions of them in the Frieza saga and the buff eternal dragon they summoned named Porunga. The Namekian Dragon Balls offered three wishes to the users, but only if they could speak the Namekian language, was a neat little twist to the storyline that later played an important role during Goku’s fight with Frieza.
While Dragon Ball Super is still early in its run, one would hope it will take the valuable lessons learned from Dragon Ball Z Kai and make better use of the Dragon Balls. There’s so much that can be done with the power of Dragon Balls. It would be a shame to see their role continuously reduced to bringing the cast back to life over and over again.