One thing that Justice League Dark (and entire animated DC universe) manages to capture that live-action superhero universes often fail to achieve is a living, breathing sense of believability.
We see how Superman operates in Metropolis, how Wonder Woman works in Washington, and how Batman deals with problems in Gotham.
There’s an organic feeling to this DC universe, and much of that has to do with the fact that we get to see the members of the Justice League operating in their cities before coming together.
Beyond that, the movie also swaps out Hal Jordan for John Stewart as Green Lantern — lending a genuine sense that other missions and adventures are being conducted that have nothing to do with the central story.