Justice League was a box office disappointment despite being a fun, occasionally spectacular action film. I believe the cause of its failure was the dour and charmless Batman Vs Superman, which turned audiences off to a sequel in the same way Last Jedi affected the box office of Solo. BvS featured an incredibly steep box office drop off for the second week, which indicated that audiences weren't going back for repeat viewings and it suffered from bad word of mouth.
Justice League is a flawed film. The opening scene with Wonderwoman where she parries the bullets from the machine gun looked really stupid, and the song "Everybody Knows" sounded really cheesy and melodramatic with that montage. The scene with the robber looked bad as well, and set a bad tone for the rest of the movie.
The dialogue was a little dopey and wasn't as sharp and incisive as BvS. Clearly Terrio overreacted to the accusations that he was a humorless writer and as a result Justice League comes across as kind of lame. The plot isn't interesting and the macguffin seems so cliched and uninspired.
I thought Steppenwolf was pretty cool, and i liked the way he bulldozed through all the opposition, but I can see why audiences might not have liked him because he was fake looking and had no personal connection to any of the heroes.
The climax was good, but the battle against Steppenwolf becomes too easy once Superman arrives, he kills any sense of danger and tension. Supermans resurrection and battle was highly contrived, with Cyborg turning hostile for some stupid, flimsy reason which seemed highly contrived considering he never loses control again.
Overall its fun but dumb, seeming like a lame imitation of the much more dramatic and charismatic Avengers. They made a big mistake by trying to rush their group film, and they should have established their heroes first like marvel did and taken their time, so there was synergy between the individual movies and the team effort. Its not an awful film and is actually quite good, but its biggest flaw is that it isn't great. It disproves the saying that you can make any film into a blockbuster with enough special effects, and demonstrates that audiences crave great stories and not empty spectacle. 7/10.