So Independence Day but with the Justice League?
Whatever you are, be a good one.

The climax could borrow some ideas from
Thor: The Dark World
. Have them fighting in one place at first but then being separated when the boom tubes transport them elsewhere.
This could also open some comedic opportunities if someone like the Flash got a hold of a Mother Box and started messing about with it, causing the other characters to be randomly transported across the world.
I think this would be a great scene in the film. For example:
Aquaman is in one place and throws his trident at a parademon. The parademon ducks, causing the trident to be sucked into a boom tube and forcing Aquaman to fight with his fists.
Elsewhere, WW is fighting more parademons. The parademon attacks, but WW ducks, before a boom tube opens behind her and the trident flies through and kills the parademon.
"How come nobody's ever tried to be a superhero?" - Dave Lizewski, 2010.

Batman would have to be with someone though.

Would be cool to have the team divided across the globe, each having to deal with shutting down their area's boom tube, showcasing their powers. then of course uniting when Steppenwolf arrives.
=w=

I would love to see Batmans reaction to parademons coming in through boom tubes.

Another way to differentiate it is to take advantage of the Boom Tubes. So instead of a bunch of ships coming from above to invade the planet, you have a bunch of portals popping up everywhere that these Parademons can fly through.
| The
Five-Star
Man || The
Golden
God |

Ummm. Maybe It's because the movie is about the main characters?

Not Zods message, but a proper attack. Millions of parademons attacking millions of civilians and even wild animals. Like a superhero version of independence day.

You mean like they did in "Man of Steel"?

Exactly. Warner bros want a realistic tone, so aliens need to attack the whole globe.
Not just new York like the Avengers, which was still a great film. But Loki should have opened portals all over the world.

That would be cool. It's kind of silly in most invasion films where the aliens just conveniently appear where the main characters are.