Audience-Alienating Premise: The show tried to appeal to both comic book fans and the Dawson's Creek crowd. This failed because the comic geeks were turned off by the unnecessary drama and pointless changes, and the teenyboppers were confused by obscure comic book references they didn't understand. Funnily enough, though, Arrow a decade later was a massive hit, and used essentially the same premise (CW drama mixed with DC Comics). That Arrow had the fortune of launching in the wake of the massive success of The Dark Knight Trilogy probably helped.
The show has gained minor trivia fame among DC fans as "the one time Mark Hamill played the Joker in live-action"... except he doesn't. His voice is just dubbed over the actor who does play him in his one scene.
"Prey for the Hunter": Detective Claude Morton is a transfer cop from Bludhaven's PD who in actuality is a Serial Killer of Metas. Morton copies his victim's mutative powers before turning them against his victims and horribly killing them, racking up a sizable victim count of criminals and innocents alike. When he's ousted by Huntress, Morton derides his partner as a "disappointment" for refusing to shoot Huntress and reveals that not only is he a Meta as well, but he's seeking to commit genocide on his own kind simply so he can live in a world free of "freaks".
"Gladiatrix": Malcolm Lagg is the misogynistic owner of the titular illegal fighting club. To keep his club running, Malcolm has Metahuman woman kidnapped and uses a drug to give them uncontrollable rage to make them fight to the death for the amusement of both him and his customers. Any fighters who don't strike the killing blow on their opponent are tortured to death for disobeying him. A Control Freak of the highest order, Malcolm also uses electric shock collars which inflict horrific pain to keep his fighters docile and under his control.
Fan-Preferred Couple: Despite the fact that Helena Kyle ultimately gets together with Detective Jesse Reese towards the end of the show, most fans prefer to pair her with her friend and mentor, Barbara Gordon. This is mostly due to the chemistry between the two's actresses, the fact that Reese doesn't exist in the comics, and the Les Yay between them. As well as the absence of Barbara's canon love interest, Dick Grayson. This only increased following Crisis on Infinite Earths (2019), where the two were the only ones from the show to return. The pairing dominates what little shipping fanfiction there is of the show.
Harsher in Hindsight: The entire storyline with Dinah and her mother becomes uncomfortable to watch after Lori Loughlin's arrest in 2019 following her allegedly having her daughter cheat on College entrance exams.
Joe Flanigan (who played Sheppard in Stargate Atlantis) guest starred as Detective Claude Morton. He and Reese are walking along discussing meta-humans and Morton says "I've seen perps who can shoot lightning from their fingertips, drop from ten stories, or turn into bugs." Reese replies "One big bug, or lots of small ones?" Morton just says "Both." Amusing in context, but if you're a Stargate fan, hilarious. In the Atlantis episode "Conversion", Sheppard gets infected by a virus and starts to turn into a big Iratus bug. In the SG-1 episode "Bane", Teal'c gets infected by a parasite and his body slowly turns into a cocoon for hundreds of similar parasites. So, now, he really has seen both.
Harley Quinn is, more-or-less, the Big Bad in this series and the top crime lord in Gotham. Come the next live-action adaptation, Birds of Prey (2020), the roles are exactly the opposite: Harley Quinn is the main character (despite having little to do with the actual Birds of Prey in the comics) helping to form the Birds of Prey as she goes against Gotham's top crime lord.
Here, Shemar Moore plays Jesse Resse, a cop confused by the weirdness, including Helena, going on in Gotham City, including not knowing who Batman is. In the DC Animated Movie Universe, he voiced Cyborg, who'd technically be a part of said weirdness and given it's based on the New 52, the DCAMU sees Cyborg replace the Martian Manhunter as a founding member of the League and thus Vic frequently works alongside Batman.
One that flies under most people's radar, the show positioning Huntress (albeit, Helena Kyle/Wayne rather than Helena Bertineli) as a prominent member seems just par the course...except the show came out in 2002, a year before Gail Simone's run made Helena a regular feature. She'd appeared in the book briefly beforehand during one of the miniseries prior to the ongoing, but until 2003 the Birds of Prey book was ostensibly a Black Canary ongoing with Oracle as her deuteragonist, and that was it. In retrospect, it makes the depiction of Dinah in the show even weirder.
Just Here for Godzilla: Mark Hamill dubs over the actor playing the Joker in a flashback. Some people will have only heard of this series because of this.
Les Yay: This time leaning FAR more towards Huntress/Oracle.
Moral Event Horizon: Harley Quinn crosses this in this continuity with the whole Guy plot.
Narm: After learning that Harley Quinn has stabbed her love interest, Wade, the face Barbara makes is supposed to be devastated... but the expression the actress makes is more of a pouty look of disgust, like she ate something that she didn't like, making it comical.
One-Scene Wonder: The Joker, who only appears for one flashback scene to shoot Barbara in a recreation of The Killing Joke, but is memorable mainly because it's technically the only time Mark Hamill has played his iconic role in live-action (his voice is just dubbed over the actual actor's).
"Knock, knock. Who's there? Batgirl... Past tense!" *Evil Laugh*
Sacred Cow: Dina Meyer got the most love of the three leads due to her character being Truer to the Text the most. She's also by far seen as the best live-action Oracle, by which we mean only, as other live-action depictions of Barbara Gordon stick to her Batgirl days.
The Scrappy: Dinah got the least love of all three leads due to being a whiny teenage girl filled with Wangst. Her being the least accurate to her comic counterpart doesn't help her case either.
The In Name Only aspects of many of the characters, notably Dinah and Lady Shiva, both of whom received a heavy dose of Adaptational Wimp compared to their comic counterparts.
Harley Quinn as the series main villain being turned into a more sinister long-term planner who is out to control Gotham and gain revenge for the Joker's imprisonment and does't ever wear the trademark costume (until the finale, and even then it was only remotely similar) or possess the bubbly personality associated with her was not exactly what fans of the character were hoping for the character's live-action debut.
The backstory of the series including the death of Catwoman and Batman abandoning the city to go into exile. The first part was seen as fridging at best and the latter significantly Out of Character for Batman, as despite the trauma of his long-time lover being murdered, trauma and loss tends to drive Batman, not cause him to shut down. Stranger still is the fact that he apparently left Gotham completely undefended in his absence, as Helena was a teenager at the time and Barbara had recently been crippled, meaning no-one was protecting Gotham until Helena became an adult. This gets even stranger when one considers this Batman trained at least three Robins, yet they're completely absent too.
The focus on metahumans in the series was seen as taking too much after shows like Smallville as whilst they have existed in Gotham they aren't a particularly heavy focus of most stories in the setting. The fact that Catwoman, traditionally a Badass Normal, was made a metahuman in this series is also a point of contention.
The Masquerade nature of the series and its past events was a little hard to swallow for a lot of viewers, mainly in how it seemed to stretch the Willing Suspension of Disbelief for such a thing. People not knowing metahumans existed is one thing. The entire city not knowing Batman ever existed despite the series continually showing more and more elements of his traditional mythos were present? Significantly harder to swallow.
They Wasted a Perfectly Good Character: Although all of the first three Robins are confirmed to exist and it's subtly implied that Jason didn't suffer his comic book fate, they remain offscreen. Even if they did remain The Ghosts, talking about Barbara's relationships with them could have been good world building. Instead, Dick is only mentioned twice and Tim and Jason get a single mention apiece.
They Wasted a Perfectly Good Plot: Some believed that the show got Dinah and Helena's roles mixed-up. Essentially, if the show had been following a more traditional approach to the characters, Dinah as the Black Canary should have been the older experienced hero, whilst Helena should have been the youngest of the group and the one in desperate need of training. The fact that Dinah actually is a metahuman in the comics means they could have kept Helena's status as a metahuman in this series unchanged and made Dinah into a mentor figure for her.
