6. A Galactic Enemy
The DC cinematic universe could start with a bang facing off with Darkseid, and while DC will take some criticism for having a villain too similar to the one introduced at the end of Marvel's Avengers. It's public knowledge that the creators of Thanos copied the design from DC's Darkseid. However it doesn't change the fact that he was always considered a threat of epic proportion to the DC universe, and since Thanos will be the main villain in the third installment of the Avengers, it would be to DC's advantage to steal some of that thunder, Shazam! With the destruction and mayhem in Man of Steel bringing in Darkseid would make the most sense. It would be an accurate depiction of the kind of disaster both in size and scope that the Justice League would have to deal with.