These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Alternate Character Interpretation: Livewire. Now, the main view is that she's a belligerent mean-spirited bigot who became a supervillain and she has no right to be angry with Superman, having "saved her life after all." However, her last facial expression conveys the emotional expression of someone anticipating, with glee, a lethal event. And not only did Superman steal that from her, he ultimately robbed her of her biological humanity.
Animation Age Ghetto: Most of the series was made to the producers satisfaction, but they were forced to change Supergirl's introductory episode (See What Could Have Been on the trivia page) and obscure Maggie Sawyer's sexuality (See Hide Your Lesbians on the main page) because they were deemed inappropriate for a children's show.
Cant Unhear It: While not quite to the extent of Kevin Conroy and Mark Hamill (as Batman and Joker, respectively), Clancy Brown is often seen as having one of the definitive interpretations of Lex Luthor, perfectly mixing a fierce thuggishness with haughty megalomania.
Common Knowledge: "Girl's Night Out", the episode of the DCAU featuring Batgirl and Supergirl against Poison Ivy, Harley Quinn, and Livewire is commonly thought to be a STAS episode, but in reality it is officially a Batman: The Animated Series episode, according to both the episode list on the official website and the fact that it was on the BTAS Volume 4 DVD rather than Volume 3 of STAS (which included the last third of the series, including Supergirl's debut).
"Knight Time" (where Superman teams up with Robin to find out what happened to a missing Batman, even impersonating him briefly) is similarly confused as a BTAS episode.
Complete Monster: Darkseid, the Evil Overlord of Apokolips and the Ultimate Evil of the DC Animated Universe, turned his home planet into a hellhole and seeks to do the same with Earth. He is a being utterly incapable of love or empathy for anyone. He handed over his adopted son, Scott Hall, to be tortured and brainwashed by Granny Goodness, treated his loyal son, Kalibak, like garbage, and attempted to outright kill his other son, Orion while joking about it. Darkseid is also fond of conducting Cold-Blooded Torture and killing minions for failing him, or even for questioning him. Over the course of Superman: The Animated Series and Justice League Unlimited, Darkseid tried to conquer earth no less than three times. The first time he’s defeated he compensated by personally murdering Dan Turpin just to cause Superman pain. The second time, he brainwashed Superman into leading Darkseid’s armies against his adopted world, turning the Man of Steel into a pariah for years. His third and final attempt stems not for a desire for power, but solely to make Superman suffer. There’s a reason why Darkseid is one of the only villains Superman outright tries to kill.
“I hope you appreciate, Kal-El, that everything that happens from this point is on your head. The skies will rain fire, the oceans will boil, the streets will run red with the blood of billions. Only then, after your last pitiful hope is extinguished, will I end your life.”
Esoteric Happy Ending: At the end of Warrior Queen Maxima is restored to the throne and the coup plotters have been defeated and it looks like Superman got through to her about the need to think of her people and less about mates... and the moment he leaves and Lobo shows up she instantly starts pining over Lobo.
Evil Is Sexy: Livewire and Lex Luthor make sure that villainy is done with lots of exposed skin and style.
Maxima, although she isn't evil so much as she is self-centered and apathetic to everyone around her.
Fashion-Victim Villain: Almost literally; Lana Lang is at one point accosted by two female thieves wearing extremely bizarre outfits.
Harsher in Hindsight: The second episode has a passenger plane hit with a missile and nearly crash into Metropolis. To make it worse the missile was fired by a terroristnote okay so they're more like mercenaries but everyone called them terrorists in the episode.
The finale of World's Finest has the Joker firing missiles on multiple buildings, sending them crashing to the ground. While people run screaming away.
In the same episode, Martha wants to give Clark and Lana some alone time so they can talk. So she tells Jonathan that Dukes Of Hazzard is on. And who plays Jonathan Kent a couple years later in Smallville? John Schneider, of course.
Another Smallville related one in the same episode: young Clark informs Lana Lang about how he is seeing through things, she asks if he's looked towards the girls locker room. This ended up becoming Hilarious in Hindsight just five years later, when in the Smallville episode "X-Ray," Clark discovers his x-ray vision by accident and ends up inadvertently seeing into the girls locker room...directly at Lana.
In "Knight Time", Brainiac's line to Superman disguised as Batman, "You are every bit the detective your followers on the Internet believe.", has gotten funnier in light of the rise of social media sites like Twitter and Facebook and their copious use of the Memetic Badass trope.
The first episode's ending of Superman simply staring at Luthor who becomes enraged at his silence is very similar to the ending of Lex Luthor: Man of Steel released nearly a decade later.
Inferred Holocaust: In the episode "Bizarro's World" a nuclear missile detonates a few miles above Metropolis. A few months later, in "Apokolips... Now!, Part 1", a nuclear power plant melts down just off the coast. To put it mildly, the cancer rate in Metropolis is about to become... impressive.
Don't forget the Joker's rampage in "World's Finest". He blew up quite a few buildings before he was taken down.
Really everything Darkseid does is this he gives weapons to Intergang that cause considerable damage to Metropolis, attempts an class-4 Apocapolypse How on Earth, and later an class 5 by crashing a comet into it to wipe out it without breaking his treaty with New Genesis, and in the finale brainwashes Superman and turns him against Earth.
Narm: In Parasite's debut episode, when he starts absorbing Superman's energy right in front of a crowd a female bystander watching screams "Good Heavens" in a Dull Surprise manner, coming off as a little silly in an otherwise serious scene.
"Prototype" has the infamous moment where Superman is temporarily blinded by the insane Sergeant Mills, leading to a bunch of sporadic piano music to start playing, but instead of coming off as creepy it's unintentionally hilarious - as is the way Superman gets smacked around by Mills while blinded.
Superman's Roaring Rampage of Revenge on Apokolips in Legacy comes to an unintentionally hilarious halt when the Furies appear and Superman actually tries to ignore them after he got done killing a bunch of Parademons with his heat vision, so they just attack him anyway and he actually lets them cling to him as they try to kill him and he continues to allow them to go on attacking him until he just crashes into a nearby statue. His encounter with Granny Goodness is also pretty bad and ends up not being as chilling as it was meant to be. TV censorship at its worst.
The Scrappy: Considering the way he thought Superman "betrayed" him in the finale and his subsequent Face-Heel Turn in Justice League Unlimited, it's highly doubtful you'll find someone who likes Professor Hamilton ever again. Bruce Timm stated in his Modern Masters book that THEY didn't like Professor Hamilton in the first place. That's why, when debating who Darkseid should kill, they finally came up with Dan Turpin, because they weren't allowed to kill Ma and Pa Kent and they felt if they killed Professor Hamilton it wouldn't have any impact, because they never liked him anyway.
Squick: In "The Main Man," Lobo defeats a giant snakelike creature by ripping its skin clean off its body, exposing the pulsating veins underneath.
Stop Helping Me!: When his clone DNA begins to break down, Bizarro decides to prove to the world that he is Superman by going out and committing heroic deeds. This includes protecting a building that was under attack (that was being demolished) and fixing a broken bridge (that was opening to allow a ship to pass beneath it).
Take That: Livewire/Leslie Wilkes could be seen as an insulting caricature of the kind of people who were believed most likely to hate a Nice Guy hero like Superman - mean spirited Generation X slackers who cared more about attitude and style than substance.
What an Idiot: Lois Lane in Target. She's put herself in danger multiple times, but at least usually she didn't know how dangerous it was or at least tried to take some kind of precaution. Here she knows exactly how dangerous her unknown enemy is and she's actually has police protection. During a phone conversation with Clark she suddenly realizes who's trying to kill her. What does she do? She sneaks off to confront them face to face. While Clark and everyone else still thinks she's under police protection. If it hadn't been for Luthor just happening to call Clark to give him a vital piece of information she would have been dead by the end of the episode.
In "The Main Man," she goes after Lobo with a metal pipe...after she's already seen him shrug off multiple punches from Superman.
Pre-Livewire Leslie Wilkes for thinking it was a good idea to hold a gathering of her fans in the middle of a storm. Look where that got her...