Injustice 2: My Dream Line-Up
Injustice: Gods Among Us was a fun game that pitted DC heroes and villains against other heroes and villains, either in support of or in rebellion against a global dictatorship run by Superman, driven to extreme measures by the machinations of The Joker. There has been talk of a sequel and, if there is, they would surely expand the roster of playable characters. These are the characters I believe should be available. Some are from the original game, some are new. Some obvious, some... not.
A plot? Well, who knows. Perhaps the Superman of the alternate reality finds an ally within the Phantom Zone who helps create a bridge to the mainstream reality, bringing the conflict to "our" world. I don't know, I'm not a writer.