Originally meant to be the lead-in from Justice League to Justice League Unlimited, Crisis On Two Earths was rewritten to be the first genuine movie of the JLA. Where as The New Frontier was more of a Silver Age story where the characters all got together in the end, this one has the League already formed in it. Although the word "crisis" in the title might give off illusions of epic crossovers featuring heroes from every timeline, the story only deals with the regular DC universe and one parallel to theirs. Also, this movie has no connection to any of the other previous DC Universe animated movies.
The Justice League as we now it has just recently set up business in this storyline, but unlike most other animated versions in recent years, Hal Jordan is the Green Lantern in this group. They are visited by a good Lex Luthor from an alternate reality where he is the surviving member of his world's superheroes. There, the JLA are the Crime Syndicate, with evil counterparts to Superman, Wonder Woman, Batman, and so on. Luthor convinces the League to come back with him to defeat the Syndicate. They manage to take down a few of the Syndicate's sub-groups, as well as Ultraman(evil Superman), which turns out to be ultimately pointless as they are all released from prision because of the hold that they have on this world. After chatting with President Slade(aka: Deathstroke or "Slade" from Teen Titans), Martian Manhunter forms yet another one of the weird pairings that the DC animated stories have with its characters by dating the Chelsea Clinton of this universe, who is really Ravager back home. Batman's evil twin of Owlman meanwhile plans to use Luthor's dimensional-hopping tech to create a doomsday device that will destroy every universe once he locates Earth-Prime, the Earth that all other realities stem from. Batman is able to stop him in time, and order is restored to the counter-world. On their return, the JLA opens up their doors to some new members.
This movie like the other DC Universe productions was produced by Bruce Timm, plus Super Friends alumni Alan Burnett. The original concept was written by Dwayne McDuffie from Static Shock and Ben 10. The animation is pretty standard of the previous DC DVDs, of which the character designs are similar too. There aren't any of the regular voice actors you're used to though in it, although Gina Torres as the sultry Superwoman(evil Wonder Woman)and James Woods as the sadistic Owlman absolutely steal the show. It's refreshing to see some of the DC heroes featured that they've never animated before, like Looker and Halo, even if its is their evil counterparts. The special edition DVD and Blu-Ray also has a bonus segment they'll be adding to future releases of Showcase where they do a short film of some of the lesser-exposed comics characters, this time around with an awesome grindhouse-like take on The Spectre. I'd recommend this one to all comics fans and superhero fanatics!