Adaptation Displacement: For a lot of people, the DCAU is the definitive portrayal and rendition of the DC Universe, and this is especially the case for the minor characters and villains introduced within the show, which being that they were obscure and known only to "hardcore" superhero comics fans before, meant that for many these cartoons were the first introduction:
Green Lantern especially suffered from this, and still does. At the time Justice League aired, Hal Jordan had been dead in the comics and made into a villain via Parallax, and he had been replaced by Kyle Rayner (who appeared briefly in Superman: TAS). For reasons of diversity, and for the greater freedom an obscure character would give them, John Stewart became the GL of the DCAU and, for most kids and teenagers, John Stewart became the Green Lantern, a fact which became apparent when in the run-up to the Ryan ReynoldsGreen Lantern (2011) film, many fans complained of whitewashing. The commercial and critical failure of that film still means, that in any media, John Stewart is still the most popular and famous GL among a good number of non-comics readers (aka most people) even if his comic book counterpart is quite different from the DCAU version.
Shayera Hol/Hawkgirl also became subject to this. She was always a Satellite Character to Hawkman and her character was weakly developed, yet the show's take on Hawkgirl became so popular and iconic, making her into an Anti-Hero who had a tragic arc that gave her much Character Development and changed the team's dynamic, that those who came to the comics often found it surprising that it was so different from the cartoon.
In Unlimited, you have the show's version of The Question which is amusing because before he had been overshadowed by Watchmen, and in a case of Recursive Adaptation, the show's version of Question is more similar to Rorscharch than Ditko's take. Nonetheless, he became a highly popular Ensemble Dark Horse.
Tom King noted that when he worked on Mister Miracle in 2017, he was inspired as much by "The Ties That Bind" as he was by Jack Kirby.
In the case of the villains, the DCAU's take on Lex Luthor, The Joker, Darkseid, Vandal Savage, Brainiac, and the other villains featured are seen as definitive by both comics and cartoon fans, with the defining voice-overs, great designs, brilliant portrayals, memorable one-liners, and many awesome and dark moments.
Archive Panic: Good luck watching the whole franchise from start to end. Leaving out the two webseries, the series totals 384 half-hour episodes and four feature-length movies. That's roughly six days. The tie-in comics add another 271 comic book issues.
Common Knowledge: A casual fan might mistake Teen Titans (2003) as part of the franchise but that's not the case, but the art styles were similar just enough for the mistake to be made.
Complete Monster: In true DC style, the DCAU is replete with heinous villains: see here.
Creator Worship: Fans hold the cast of this franchise sacrosanct: Kevin Conroy and Mark Hamill are the most obvious, but even minor actors, such as Michael Rosenbaum (helped obviously by his time in Smallville) are also ensconced. The current massive popularity of Harley Quinn has led to a cult of Arleen Sorkin as the "true" Harley. Even the background creators, such as Bruce Timm and Paul Dini (who wasn't even part of the initial crew), and in particular Andrea Romano, the animation and casting director who brought all these icons together in the first place, are beloved by fans.
Fandom-Enraging Misconception: DCAU refers to specific series and films, but many people mistakenly use DCAU to refer to wildly different animated media such as the DCAMU and the Tomorrowverse.
Fandom Rivalry: With the DC Extended Universe and especially the films by Zack Snyder. Many fans claim that the DCAU was the perfect blueprint for a live-action Shared Universe while having a better understanding of Superman and Batman, in spite of the fact that Bruce Timm himself has been very supportive of Snyder and approved of many of the stories Snyder explored in his films.
Fan Nickname: The DC Animated Universe has also been referred to by fans as the Timm-verse and to a lesser degree, the Dini-verse (as Paul Dini's involvement in the series had somewhat lessened by the time of Justice League).
It's a fact that across the entire franchise, they used a possessed Superman and Beware the Superman fears on four occasions — "Brave New World" (Superman TAS: Alternate Universe where Lois dies and Superman becomes Luthor's enforcer), "Legacy" (Superman TAS: Darkseid brainwashes Superman), "A Better World" (Justice League: Alternate Universe where the League rules the world), "The Call" (Batman Beyond: Superman is mind controlled by Starro). The Cadmus arc in Justice League Unlimited, meanwhile, doesn't actually feature a rogue Superman but is motivated by paranoia resulting from the events of "Brave New World" and "A Better World". While this trope and its use was criticized even by fans, and even Timm admitted they depended on it too much (and was self-critical especially about them using it in "The Call" to serve a plot twist), it was at the very least not lingered on too much, and was balanced by more heroic and awesome Superman moments. Later writers have continued to draw from the Beware the Superman well, however. For instance, the highly popular Injustice games and tie-in comic series feature Superman as a main villain, and the DC Extended Universe feature the trope along with Destructive Savior to such an extent that the idea of Superman as an icon of hope may as well be an Informed Attribute. Many fans worry that these high-profile stories have damaged Superman's brand because among a good portion of the public, the evil Superman has become just as familiar as the regular one.
Likewise, the creators of the DCAU used the trope and concept in order to successfully present Superman as a well rounded three-dimensional character in addition to giving him a dramatic arc and tension that the Richard Donner films and other adaptations don’t have. They portrayed the DCAU Superman as being heroic, powerful yet flawed, human, likable, and relatable in addition to giving his story a tragic dimension (as the DCAU Superman goes from being naive, friendly, and likable to being paranoid, short-tempered, and aloof), much like how they had the DCAU Batman develop from being nice and friendly (in Batman: TAS) to being cold, distant, and standoffish (in The New Batman Adventures and to a slightly lesser extent Justice League) in order to show the psychological impact of the superhero career on their characters. The later writers outside of the DCAU handled the idea of a flawed Superman without this subtlety, seemingly making Superman evil for the sake of cool costumes or because "antiheroes are more interesting", when the point of the DCAU Superman is to present that, despite his flaws, he is heroic, likable, reflective, resists becoming dour, and in the end would never give up his moral code.
Gateway Series: The DCAU is the first faithful and high production versions of many parts of the DC Universe that had been little known or unrepresented at that point:
In the case of Batman, it provided many people's first glimpse of the less well-known parts of his Rogues Gallery, namely Ra's Al Ghul and Scarecrow (neither of whom had appeared in movies at the time or in the Adam West shownote Ra's was created in 1971 well after the show was over, and Scarecrow was too scary and dark to appear on the show), as well as Killer Croc, Scarface and Ventriloquist, and redefined and updated the likes of Mr. Freeze to the point that it quickly became his origin in the comics and wider media. Poison Ivy, while popular today, wasn't as well known back then until this show brought her mainstream attention.
Likewise, Superman whose movies tended to not accept the existence of bad guys not named Luthor and Zod, his cartoon introduced many to Brainiac, to Mr. Mxyzptlk, Toyman, and the Jack Kirby Fourth World and his extended cast: Dan Turpin, Intergang, Darkseid, Apokolips, New Genesis, the Mother Box, Boom Tubes and other amazing concepts. Likewise, the DCAU version of Luthor was the first one to emphasize his scientific acumen (which the movies never tackled) and his Corrupt Corporate Executive revision of The '80s (or as Neil Gaiman called him "skinny Kingpin").
Justice League served as many people's exposure to the wider parts of the DC Universe, proving their first introductions to the Flash, Green Lantern, Wonder Woman, and Hawkgirl among many others. Likewise it introduced them to Amanda Waller, Suicide Squad, Vandal Savage, Despero, Amazo, and others.
Hype Backlash: The DCAU is put on a high pedestal. Its descriptions of characters are called the definitive versions by a number of fans. Every other superhero animated show and/or film (and even live-action versions) are compared to it. As a result, some people can be confused by the praise and find it So Okay, It's Average. It doesn't help many other superhero shows borrowed from it, making a lot of elements that were Once Original, Now Common.
Most Wonderful Sound: The DCAU had a lot of these, but Superman's takeoff sound is a prime example. It's so memorable it was carried over into other animated adaptations.
There is also the sound of Wonder Woman's lasso of truth whenever she is using it in order to catch someone.
The DCAU (and Bruce Timm as a side effect) has a shame for nerfing Superman, at least in the eyes of fans who came to the series from other versions first (newcomers initially couldn't tell the difference). This was especially visible in the first season of Justice League. Later on the writers improved in their ability to write Superman as a more powerful hero in Justice League's second season onwards and more importantly made that supposed weakness an iconic moment. However, the Timmverse still has that reputation for portraying Superman as a weakling and overly favoring Batman. Of course, Superman's power-levels have always fluctuated Depending on the Writer in the comics and movies and, in the case of the DCAU, the writers made a deliberate choice to depower him to make things interesting. Going back to Superman: TAS, they stated that the DCAU Superman could very possibly be killed just from an excessive application of force without ever needing to use kryptonite.
As beloved, cherished, and memorable as DCAU Batman is today (even now, you'll still find quite a lot of people who consider Kevin Conroy's Batman to be the definitive animated Batman), his relationship with Barbara Gordon in Batman Beyond is something that'll always remain one of his most controversial acts, especially considering Barbara was in a previous relationship with Dick Grayson, Bruce's adoptive son, who still had feelings for her and was hurt badly enough to fall out with Bruce after finding out she was with him. While you might find a few people here and there defending the Bruce/Barbara relationship by saying it was a consensual relationship between two legal adults and that Dick was never Bruce's biological son so the relationship shouldn't have serious incestuous overtones, Batman entering into a relationship with Batgirl is still by and large considered a very notable and heavily discussed black mark on an otherwise beloved and iconic All-Loving Hero who dedicated his life to saving lives and helping others.
Periphery Demographic: While technically meant for kids, the DCAU from the very beginning had been just as popular with teens and adults due to the good action, clever writing, interconnected story, partial comic book accuracy, multi-series continuity, surprisingly dark themes, great animation, excellent art style, and generally taking its audience seriously. Many Cartoon Network DC shows have yet to live up to it (apart from maybe Young Justice (2010)) due to being much more kid-friendly. Fortunately, this was very likely why the DC Universe Animated Original Movies line was launched, which was made as the Spiritual Successor to the DCAU (especially the DC Animated Movie Universe), and caters specifically to that Periphery Demographic, and their old demographic as adults, with a Darker and Edgier yet still well-done style to match. However, Lobo (Webseries) averts it all for an adults only cartoon with strong profanity, sexual humor and graphic violence.
Tough Act to Follow: The multi-series continuity, art style, great writing, brilliant animation, partial comic book accuracy, and voice work of the DCAU ensures that successive series, ranging in quality, have a very high standard to meet.
It has also come to enjoy a reputation of standard for even the live-action films, with many critics comparing Batman v Superman: Dawn of Justice unfavorably to World's Finest and Justice League (2017) poorly to the animated series, noting how the animated series succeeded in making Superman and Batman flawed and relatable, yet heroic characters, which the movies also aimed to do but failed to properly execute it and to control the tone, resulting in both characters becoming unlikable. They also believably made the formation of the League something which served a team dynamic, and convincingly created threats that allowed everyone a chance to shine. The release of Zack Snyder's Justice League had a better portrayal of the team in a film.
What Do You Mean, It's for Kids?: While technically a franchise meant for kids, it's pretty clear that teens and adult viewers and comic book fans were the intended audience by the creators. In particular, there are so many double entendres that the wiki has an entire article about it. There's also drugs, racism, abuse, onscreen deaths and violence (the Hit Flash used in other shows to censor violence is completely absent here), and towards the end when it was relegated to late Saturday nights as opposed to getting afternoon airings on regular days, they didn't even bother trying to act like it was for kids anymore.
Viewer Gender Confusion: Granny Goodness is a woman, but the fact she's both visually based on and voiced by Ed Asner makes it a little hard to tell.
. There's also drugs, racism, abuse, onscreen deaths and violence (the Hit Flash used in other shows to censor violence is completely absent here), and towards the end when it was relegated to late Saturday nights as opposed to getting afternoon airings on regular days, they didn't even bother trying to act like it was for kids anymore.