Great premise to this two-parter. Starts off very fast with the two heroes realizing they are in some alternate world where Metropolis and Gotham are one - Gothamopolis. All the villains are combinations like Doomsday/Deathstroke = Doomstroke. They also meet the Justice Titans.
And in the next issue, the solution to how this happened is better than you think it'd be.
Very fun and lots of action and originality.