12 Reasons Why Justice League Is Worse Than Batman V Superman
12. None Of The Heroes Have A Character Arc
Although a lot of critics argued that the motivations of the two heroes in Batman v Superman were simply a contrived way to get the iconic characters to fight, at least you understood their reasons for doing so. Bruce Wayne's introductory scene clearly establishes his fear that Superman could cause more harm than good, an idea he wavers on as the film progresses.
You might argue that this arc is entirely out of character, but at least it's an arc that makes Batman an active participator in the plot, unlike in Justice League which struggles to find any personal motivation for the actions of any character, not only the Caped Crusader.
While they're all ostensibly motivated by the potential end of the world, Batman is just spinning plates, while Aquaman's Atlantian history is never brought up outside of one brief scene. The Flash has a few instances of growing into his heroic role while Cyborg struggles with his new body, but even these better-developed characters aren't given complete arcs and are forgotten about by the end of the flick.
It leaves every member being short changed, and none of them feeling like they need to be there.