WARNING: Similar to the brilliant and highly recommended, Batman: Under the Red Hood, these films are for adults only. Parents should watch them before deciding if they're appropriate for their children.
The classic origin of the Justice League of America (JLA Vol 1, #9) brought Superman, Green Lantern, Aquaman, Wonder Woman, Flash, Batman and Martian Manhunter together to fight an invasion by aliens called the Appelliax (reference to this origin is made in the several episodes of the animated series Young Justice). The most recent revision of the DC universe, called The New 52, tweaks this story so that the invading force is from the hellish planet Apokolips, Martian Manhunter has been replaced by the pre-52 Teen Titan, Cyborg (aka: Victor Stone), and Shazam (aka: Captain Marvel/Billy Batson) is added to the line up. JL: War is the animated story of this new origin.
The animation in War is passable, but not impressive. The voice acting is weaker than many of DC's other productions as well. I'm a huge fan of Alan Tudyk; his work as Green Arrow in both Young Justice and Injustice: Gods Among Us is perfect for his tone and humor. Unfortunately, he was cast as Superman for War and his vocal skills can't carry the strength and authority needed for Big Blue. Jason O'Mara's Batman sounds like a flat imitation of Bruce Greenwood's Batman from Young Justice and Red Hood; in his defense, Greenwood's Batman is one of the best since Kevin Conroy's classic Batman: TAS, so if you're going to imitate someone, he's it. The most significant downside to War is, unfortunately, the writing. With the notable exceptions of Cyborg and Flash, the Leaguers are all immature at best. They just aren't heroes. Even Superman revels in his power and superiority too much to be the role model he should be. At one point Wonder Woman chides Shazam for being immature, but since she, GL, Superman, and even Bats are so childish themselves, the condemnation strikes hollow.
JL: War is a basic introduction to the modern origins of the League and if you're going to give it a shot, I recommend watching it before the far superior, Flashpoint Paradox.
Flashpoint focuses on the rivalry between Barry Allen and his time-traveling nemesis, Eobard Thawne (aka: Professor Zoom). Barry wakes one day to find the world he knew replaced by one on the brink of destruction. Atlantis and Themyscira are at war with the surface world and each other. Worse yet, the accident that gave Barry his connection to the Speed Force never happened so he can't do much to stop it. Other heroes lives have also taken dramatic turns.
I don't want to spoil the twists, but I was shocked by the fascinating and brutal events the time-shift creates. This is not your standard What If time paradox. The animation is better than War, but still not the best in the DC library. The voice acting and dialogue is far better than War, with the return of fan-favorites Dana Delany as Lois Lane, Nathan Fillion as Green Lantern, Vanessa Marshall (Black Canary from Young Justice) as Wonder Woman, Kevin Conroy as Batman, and Superman Classic Tim Daly's son Sam Daly voicing Big Blue. Fronting these powerhouses is an impressive debut by Grey's Anatomy's Justin Chambers as The Flash.
Flashpoint Paradox is even less accessible to younger audiences than JL: War. The combats are lethal, the story complex, and the turns in characters' lives are depressing at best. Having said that, the uplifting final scene touched me like few other stories have.
Flash fans will love that Barry is finally featured in his own film. More than just an origin story, this film gives insight into the lives of many of your favorite DC characters. A great introduction to the Flash legend, Arrow fans in particular will find this a solid primer to the spin-off Flash series later this year.