10. Fully Introduced Its Main Characters In Previous Films
None of Justice League's main heroes disappointed as such. Aquaman could have been a laughing stock but was edgy and cool, Ben Affleck struck a balance been the gritty, joyless Batman in Dawn of Justice and something closer to the comic books, and Wonder Woman was in fine form once again.
The Flash's youthful energy and wise-cracks were a welcome addition to the franchise, and Ray Fisher's Cyborg added a slice of life to the story when he completed his journey to self-acceptance with the help of his teammates.
The only problem is that in Aquaman, The Flash, and Cyborg's cases, there isn't enough of this stuff, and that's purely because Warner Bros raced towards the finish line quicker than Superman and Barry Allen in that post-credits sequence when putting Justice League together.
Desperate for a Marvel Cinematic Universe killer, the studios fast-tracked its team-up movie without putting in the necessary groundwork. Ideally, all six heroes should have been given solo outing ahead of the main event.
The Flash's backstory involving his imprisoned father needed fleshing out, and plumbing the depths of Atlantean lore - as the series did with the Amazons - beforehand wouldn't have hurt. Cyborg is the biggest victim of Warner's haste as his character arc is more complex, and much of it had to be glazed over.
Victor Stone's journey from self-loathing to self-acceptance should have been inspiring, and his strained relationship with his father could have amped up the conflict and emotion, but there simply wasn't the screen time to do justice to any of that.
All of the above should have been laid out in Aquaman, The Flash and Cyborg solo films before Justice League arrived in cinemas. That way, every member of the team would have been on an equal footing without the need for rushed introductions.