The annual Arrowverse crossover, although not a movie, had it all and was hands down better than the $648.4 million Justice League.

A good superhero movie needs to have cool superheroes, even better antagonists and extended background plots on each of them. When it comes to building extended timelines throughout multiple movies, Marvel has been the boss by a long way.
The MCU timeline came into existence with the release of Iron Man (2008). Since then, each film has been subtly adding to the larger plot while still maintaining the essence of the story. 

Where did Justice League go wrong?

DC Comics recently began clubbing all the pieces together, with Batman v Superman: Dawn of Justice marking the beginning. But we only had a solo Wonder Woman movie before DC decided to go all in with Justice League. It was too soon. Earlier, we had a Batman Trilogy directed by Christopher Nolan, but apparently they weren’t timeline-worthy. 
When you speak of Iron Man, you think of Robert Downey Jr., similarly Chris Hemsworth for Thor. The same cannot be said for DC’s heroes. Batman alone has been played by nine different actors (including voice-overs), and Superman by 10 of them. What DC has been lacking throughout its movie franchise is consistency. It needs to step up it’s game by maintaining a constant flow in the timeline.

The Prospect Of Steppenwolf

The Flash, Aquaman and Cyborg were not given a proper introduction, not to mention the ridiculous appearance of Steppenwolf.
Although Flash, Aquaman and Cyborg will have their solo films out in the future, Justice League didn’t do them justice. The solo films should have been the anchor on the basis of which Justice League stepped into the limelight. You cannot expect the viewers to emotionally attach themselves with any of the characters unless they have their own background plots.
Moreover you cannot expect the audience to hate a CGI based super villain who suddenly appears out of nowhere. Steppenwolf needed a better introduction before being sent off to blow the world. Steppenwolf is a powerful character in the comics, the general of Darkseid. It is only fair to the character to give him a proper story before slapping him on screen. But there is only so much you can do in a two hour long movie.
You can read more about Justice League’s shortcomings here.

Crisis On Earth-X Had It All

The Arrowverse crossover was better in all aspects, a truly superb team up of our favourite heroes and a group of psychotic villains. Each of the superheroes, from Oliver Queen to Ray Palmer, had their own stories. And it gave perspective to the team up. DC’s blockbuster cannot boast of that attribute. 
The CW network has been beating the DCEU timeline by far. It has superheroes with their own background stories and personal missions. It even has villains with a clear agenda and a rough history. Moreover, it has crossovers! Now, who doesn’t love a crossover? All of this was possible because CW decided to run some of their shows (Supergirl, Flash, Arrow, DC’s Legends of Tomorrow) on a similar timeline. They weren’t haphazard.
On the same lines, DC hadn’t been really serious about maintaining a timeline until Batman v Superman: Dawn Of Justice. That’s precisely where they failed.
Overall, the crossover was better than the movie considering all possible paths. If DC wants to beat Marvel, it needs to settle down and take it step by step. Considering the movies DC has lined up, the prospect of the DCEU is looking good for the foreseeable future.
Do you think Crisis on Earth-X was better than Justice League? Let us know!