Alternative Character Interpretation: Is everyone in the Legion of Doom on board with Savage's genocidal plan or are some of them just afraid of provoking his wrath after he proves they can't kill him and are then unwilling to let the Justice League arrest them in the climax. Cheetah even notes that it isn't as if they have much choice other than obeying Savage (although she does sound a bit interested discussing his new world order later on). For that matter, does Cheetah try to kill him (which proves he's immortal) just out of Pragmatic Villainy because it will ruin the world's economy and keep her from spending her bounty on Wonder Woman, or does she disapprove of his plan at least partially due to hidden moral qualms?
Broken Base: Although fans are ecstatic that the original voice cast returns for the Justice League, many felt disappointed that the Legion of Doom was altered. Either the Legion isn't as great because many of the original members are absent or it's better because we see other unappreciated characters shine in the spotlight.
Complete Monster: Vandal Savage is a conqueror with genocidal plans for Earth. He manages to steal the protocols that Batman designed to defeat the Justice League in case one or more members turn evil. Savage makes these protocols more lethal and sadistic and then uses them to take out the Justice League. After his Legion of Doom seemingly triumphs over the Justice League, Vandal Savage informs them he plans to Take Over the World by using a missile that will cause a solar flare that will kill half the world's population. This event will also render the rest of the world's population so weak and helpless that they will naturally accept his leadership.
Crack Ship: Some fans ship Batman with Cheetah, for some reason. However, the two never actually interact at all together and are never even in the same frame. This is most likely heavily influenced by a scene from the Justice League cartoon where Batman seduces Cheetah while being held captive by Lex Luthor's Injustice Gang.
Evil Is Cool: This incarnation of Vandal Savage is easily considered one of his best in media despite his genocidal goals: a suave, sophisticated, and intelligent conqueror with genius plans.
Genius Bonus: When J'onn is told that poison he drank is largely magnesium which will sweat out through his skin, it creates a special Oh, Crap! for the audience who knows that that metal is special in that it's flammable. Magnesium flames also can't be extinguished by water. Magnesium burns with a white flame!
Harsher in Hindsight: The film highlights Batman's preparation to immobilize the members of Justice League in case anyone goes rogue, fearing of what will happen if the league's power is left unchecked. However, most of the league's member object Batman's plans in secrecy, confident that they won't abuse their power and accuse Batman for not trusting the league. One year later, Injustice: Gods Among Us shows exactly what happens when a tragedy struck and those in power are left unchecked: they become world-ruling tyrants.
It Was His Sled: Anyone who's read Tower of Babel will know that the plans came from Batman, and the movie ends with him quitting the League.
Magnificent Bastard: Vandal Savage, the Big Bad, steals all of Batman's plans aimed at incapacitating the Justice League should they ever turn to darkness or prove too dangerous, taking them and making them far more lethal and dangerous. Recruiting his very own Legion of Doom, Vandal has them lure the League into traps before putting the countermeasures into placing, nearly killing every single member of the League in a single night. Vandal reveals his true plans to cause a solar flare to strike earth so he may cause the conflict that he feels is necessary for human advancement and cause the world to submit to his rule, offering to share the rulership with his new Legion. A charming, sophisticated villain, Vandal shows he has surpassed the savagery he has born into, nearly completely erasing the League in one fell stroke with the world falling perilously close to Vandal's utter victory.
Memetic Mutation: The ending of this film with Batman leaving the Watchtower after quitting the League started a meme where many fans left comments stating that because Batman's finances built the Watchtower it belongs to him rather than the Justice League, and so if he's not a member they should be the ones to leave.
One-Scene Wonder: The Royal Flush Gang is captured in the first scene but get just enough characterization and cool costumes and technology to make a big impression.
Ma'alefa'ak is strangely seductive towards J'onn, taking the form of an extremely attractive blonde woman to lure J'onn in and buying him a drink. The movie doesn't mention it, but in the comics J'onn and Ma'alefa'ak are twin brothers.
Sure it's to save him, but Martian Manhunter extending some tendrils into Superman's body to pry the kryptonite bullet out is still rather disturbing imagery.
Some fans have expressed unhappiness at the decisions to replace Aquaman with Cyborg, Kyle Rayner with Hal Jordan, Ra's al Ghul (The Big Bad of Tower Of Babel) with Vandal Savage and the Legion of Doom, and the omission of Plastic Man. The fact that, despite Michael Rosenbaum voicing the Flash, that it's Barry Allen and not Wally West (whom Rosenbaum voiced before) has also taken some people aback. Some fans who were introduced to the Green Lantern through the animated Justice League also were left with the short end of the stick with what could feel like a random replacement of Hal Jordan for John Stewart, despite Stewart not appearing in "Tower of Babel".
Lois Lane sports a starkly different model than other productions or comics, for some reason having Wonder Woman's distinctly Greek features, which has met with confusion and occasionally scorn from fans.
A lot of fans also hate the changes made to Batman's failsafes, in particular the Green Lantern and Flash traps (which were appropriately the most radically changed of the lot).
Batman choosing to quit the League rather than being voted off by the League is one for many, feeling it misses the entire point of the original story where Bruce's paranoia finally goes too far and causes him to be essentially excommunicated from the superhero community.
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