Beginning in chapter 14, Goku Black' arc had a mysterious start with the reintroduction of Future Trunks and Goku Black’s surprise reveal, but even these shocking elements received a hard time from unimpressed fans.
Chapter 14 of Dragon Ball Super titled “An SOS From the Future” marks the beginning of the Goku Black arc. This chapter begins with Future Trunks on the run from a hidden villain. A sense of dread begins to build as Trunks is continually chased through the wreckage of what is presumably West City until the villain is finally revealed in a shock twist: an evil Goku’s sinister smile wreathed in smoke and flame. This opening chapter marked a completely new turn for Dragon Ball, one surrounded in mystery and intrigue, but the arc’s resolution is generally seen as failing to live up to the promise of its introduction.
Future Trunks is a definitive fan-favorite character, so it made sense to bring his character back despite his conclusion in the 'Android Saga.' There were several possible plot threads to pick up on with Future Trunks, most notably how he would handle protecting the Earth on his own, even with his newfound power. This is touched upon in the 'Goku Black' arc, and yet Future Trunks has no real role to play in a story that is supposed to center around him. The arc’s ending pays short shrift to Future Trunks losing everyone he knew, loved, and fought tooth and nail to protect (with the sole exception of Mai), and even worse makes him seem callous for how quickly he accepts it.
At the same time, the threat posed by Goku Black ultimately suffered from coming in the form of Goku. Beyond the initial shock value he brought, the use of this character did nothing for the arc. Zamasu’s reasoning for stealing Goku’s body is completely short-sighted and he somehow completely neglects to ask Zuno, the being that knows the answer to every question in the universe, what the best body for him to steal would be. Goku Black was ultimately empty, but a character like Gohan being taken over and used to torment Trunks would have made for a much more emotional story. Future Trunks’ origin story is heartbreaking and the main villain having zero connection to his character is a complete miss.
Similarly, Zamasu could have been something completely unique to Dragon Ball, introducing a profound negative character arc, but his reasons for becoming a villain are paper thin. Instead of instigating universal genocide after watching two cavemen smack each other around, Zamasu could have easily been displaced in time and forced to live alongside mortals. Being personally subjected to cruelty would have made for a much more sympathetic and understandable reason for Zamasu considering mortals failures.
With a more fleshed-out backstory for Zamasu and a different host body that could better play off Future Trunks, 'Goku Black' could have been a genuinely exciting and thought-provoking arc right until the end. Instead, Dragon Ball's 'Goku Black' arc failed to live up to its promise of mystery and intrigue, and it fell short in setting up emotional and reasonable character arcs for its main characters.
