Reality Subtext: The Superhero Registration Act subplot reflects not only the general paranoia of the McCarthy era, but also the fact that superheroes really were under government investigation at the time the story takes place - In 1954 several comics publishers were investigated by the Us Senate's Subcommittee on Juvenile Delinquency as part of a larger moral panic that lead to the creation of the Comics Code Authority.
Shrug of God: The series takes some notable liberties on DC canon for the sake of averting Comic-Book Time and portraying the transitional period from the Golden Age to the Silver Age. So when high time came for debate on what alternate Earth the series is supposed to take place in, Darwyn Cooke drew a comic for the movie's DVD release where Rip Hunter tells everyone to not worry about it.
Rip Hunter: Who cares what world we're on? Just sit back and enjoy these untold stories from the last heroic age.
At one point, the story was going to feature an entirely original superhero named Cobalt, a woman abducted by aliens in the Forties and returned years later with superpowers in order to help fight off the Centre.
The story was meant to originally end more introspectively. Superman would've been revealed to be recovering on some island with Aquaman as his only friend there, and the two would discuss the pros and cons of humanity. Darwyn Cooke opted to remove this because it was too low-key... and gay.
Word of Saint Paul: Despite Shrug of God above, it would be years later when Grant Morrison penned The Multiversity and came up with the catalogue of the Post-New 52 DC multiverse that the series was confirmed to take place on Earth-21, and its diverging point being the survival of John F. Kennedy from his fateful assassination.
The Movie
All-Star Cast: Had the biggest one of any DC animated film up to this point, and it's still an impressive roster today.
Aquaman is voiced by Alan Ritchson, reprising his role from Smallville. In addition to that, Bugs Bunny is voiced by Joe Alaskey, reprising his role from various Looney Tunes projects, most notably Looney Tunes: Back in Action.
In the French dubnote which was done MANY years after the movie was made, unlike the majority of the DC Universe Animated Original Movies, several voice actors from other adaptations reprise their roles here:
From Superman/Batman: Apocalypse: In addition to Superman and Batman, Delphine Braillon as Wonder Woman/Diana Prince.
From Batman: The Brave and the Bold: In addition to Superman, Batman, Wonder Woman, the Flash, Lois, and Robin, Philippe Peythieu as Martian Manhunter/J'onn J'onzz, Michel Vigné as Aquaman and Captain Cold, and Nicolas Marié as Dr. Magnus.
From Young Justice: In addition to Superman, Batman, Wonder Woman, the Flash, Martian Manhunter, Aquaman, and Captain Cold, Vincent Ropion as Ray Palmer, and Michel Vigné as King Faraday.
What Could Have Been: At one point, Wonder Woman and Lois Lane's roles were going to be cut out due to time constraints. Darwyn Cooke personally intervened to keep them in, insisting that they played pivotal parts that shouldn't be cut. He even joked that the movie might as well have been renamed "White Guys in the '50s" had they been removed.