Injustice explores the perils of vigilante justice and the blurred lines between good and evil. However, instead of getting another story out of this through Batman, this time, a grief-stricken Superman is driven to wreak vengeance on the evildoers of Earth by any means necessary. It contains obvious messages about, in words the characters even use, the problems inherent in trying to be "the world's police," and such blind justice goes into some ridiculous (but unexpected and amusing) extremes, such as Superman's livid reaction when he discovers that disaffected teenagers are throwing Joker-themed raves in abandoned warehouses in Metropolis.
It's rated R, and while it isn't that much more violent and profane than all of the other noir movies of the DC Universe, there's enough blood, fighting, sound effects, and trauma to justify it, to say nothing of the language and infrequent sexual innuendo. The acting is solid, and the animation isn't of the highest quality, but it works for the story. The story itself turns into the usual snags and snarls of so many side stories and secondary mortals, heroes, and villains, to the point where the complexity is best enjoyed by the superfans. For everyone else with a passing familiarity, the biggest surprises happen when one realizes that characters are killed in this alternate universe, no matter how heroic or villainous they may be, and make this an interesting exploration of all-too-familiar themes and characters.