Alternative Character Interpretation: How much did Joker want to take over from Carl Grissom? While he did kill the man, he seems to have been motivated by revenge, with him filling his former boss's shoes as an afterthought. On the other hand, some of his comments as Napier seemed to imply that he wanted to be Grissom's successor.
Badass Decay: Despite having a minor role and being not as trim and fit as in the comics, Commissioner Gordon is perfectly competent in the Burton movies, but in the Shumacher films he's turned into a joke.
Michael Keaton being cast as Batman, and now after all these years fans still divided over him, perhaps even more so now thanks to the Christopher Nolan Batman films starring Christian Bale. Some fans still insist Keaton was, is and will always be the one true honest, most perfect definitive Batman and that no one else will ever surpass him and hate on Bale for not sounding like Kevin Conroy, while other fans still feel Keaton was miscast and will always feel he was miscast and prefer Bale for being a closer physical match to Batman's comic book self and for playing up both sides of the persona. And then there are fans who don't like either actor in the role, and there are fans who like both actors in the role, and others who feel Keaton did well enough with what he had. That's not even bringing up Val Kilmer and Ben Affleck which can complicate things even further as to who the best Batman is.
Jack Napier killing Bruce's parents as opposed to Joe Chill. Some like this change and think it adds a more personal level to the Batman/Joker dynamic. Others, like Linkara, dislike it for effectively turning Batman's arc into a revenge story against one man, as opposed to crime as a whole as symbolized by a faceless mugger.
The "mime assassins" at Ricorso's killing. They are never seen again after that scene, and are only vaguely referred to by Mayor Borg as "these gangsters." It was probably intended to be understood that these were the Joker's usual henchmen disguised as mimes, but the movie never makes that explicit.
The "Partyman" sequence in the museum could also qualify. Although it is indeed foreshadowed ("Daddy's going to make some art, darling") and serves a purpose in bringing the Joker and Vicki Vale together, it otherwise contributes nothing to the plot and is never mentioned again once Batman shows up. (Outside of the movie, this scene was just inserted to get one of the songs by pop star Prince incorporated into the movie's soundtrack.)
Vicki fainting after she sees the "flowers" the Joker brought her - or may be a Funny Moment.
The Batplane locks perfectly onto the Joker, yet none of the bullets touch him as he stands completely still. The film makes no attempt to explain why this happened. note The simplest explanation is that the Batwing wasn't designed to hit a man-sized target given where the weapons are placed.
Complete Monster: The Joker, real name Jack Napier, is an insane, sadistic criminal. Murdering the young Bruce Wayne's parents, Jack is only stopped from killing the boy himself when his partner warns him the cops are approaching. After being transformed into the Joker, Jack goes on to kill the mob boss who betrayed him, before killing the other Mafia higher ups to take over the Gotham syndicate. Using Smylex mixed in with everyday products, Jack causes a string of deaths of unsuspecting innocents. Jack also abuses his girlfriend, Alicia Hunt, disfiguring and eventually killing her, before trying to seduce Vicki Vale immediately after her death. Taking advantage of Gotham's 200th anniversary parade, Jack tries to gas the gathered civilians with Smylex to amuse himself and takes out his frustration over Batman stopping his plans by killing his loyal second-in-command.
Crosses the Line Twice/Nightmare Fuel: In what was perhaps the movie's most infamous scene, the Joker electrocutes Tony Rotelli with a "real" joybuzzer and then briefly chats with his burned, husked, and still-smoking corpse, acting as if the dead man is still alive. Kids in the audience couldn't watch that scene for years afterwards!
Critical Dissonance: With a 72% rating on Rotten Tomatoes, critics have a more divided reaction towards the film. Compare that to audiences who not only made it the second highest grossing film of the year, but fondly regard it when it comes to superhero movies and film in general, some even regarding it as a favorite or the definitive Batman/Superhero film!
Ensemble Dark Horse: Joker's right-hand man, Bob. He doesn't get very many lines in the movie, and is shot by Joker when Batman steals his balloons, but still manages to leave a lasting impression.
Fanon: While Jack Napier's partner who grabbed Mrs. Wayne's pearls is generally believed to be Bob (both actors do look similar), several fans assume him to be Joe Chill; not even the script names him.
The Joker hogging most of the screen time. Sure, it was setting up his origin story, but it would be more problematic in the later movies with their dual villains taking more time than Batman.
Use of Bizarrchitecture. Subdued and reasonable in this film, over the top by the last.
Campiness. It wasn't quite as bad here due to the seriously-taken plot and the characters, but it was still a film where the Joker pulled off comedic heists, the Batwing had giant scissors, and the final fight is between two guys dressed as a giant bat and a clown.
Fountain of Memes: Aside from the catchphrases, the Joker's initial reaction to seeing his new face (smashing the mirror, giggling madly) became widely imitated. (Example: Lisa Simpson seeing her braces.)
Batman's entire origin story becomes significantly harsher after the events of the Aurora theater shooting. It's even worse in this adaptation because of the fact that The Joker was responsible for creating Batman in the Burton/Schmaucher film continuity, since the madman who shot up the Aurora theater based his actions on The Joker.
One of the first things Batman says in this movie was "I'm not going to kill you", but doesn't quite hold to his word. In Batman Begins he says it again, and this time he does. Though to be fair, he only meant he wasn't going to kill the guy he was speaking to, which he didn't.
Ben Affleck was considered for the role of Robin before he was written out of the later scripts. Paralleling the concept of Dick Grayson as a potential successor to the Dark Knight, Affleck ends up playing Batman in the DC Extended Universe.
Misaimed Fandom: In an extremely rare case where a henchman received one, we have Bob the Goon, depicted here almost as Jack Napier's/The Joker's Heterosexual Life-Partner and a sort of proto-Harley Quinn. Fans of the movie will often mention how much they love Bob, which is pretty strange as he doesn't do much that's noteworthy and in fact (except for Alicia) is the least dangerous member of the Joker's gang. It must be the look, as Bob does look like he could be the world's hippest slacker. Even portrayer Tracey Walter himself became enamored with the character, remarking in an interview that Bob's enthusiasm really shines through: "He admired what the Joker stood for." As if the Joker were ever anything more than a delusional psychopath, not to mention that Bob is executed because (or in spite of) his loyalty.
Moral Event Horizon: As with his just-as-famous-if-not-moreso counterpart, it's not a question of whether The Joker crosses it, but when. Perhaps the most likely crossing point is killing Thomas and Martha Wayne when he was younger. As for the first crossing point to be shown? Tougher to pinpoint; there's killing off countless Gothamites with his Smilex gas, or killing Ensemble Dark Horse Bob if you liked him. It could be argued that, for the characters in the movie at least, the Joker at first appears to be a sort of Bully Hunter, since at first he stalks and murders only ruthless mobsters - guys whom all the decent people of Gotham want to see dead, but whom not even Batman will bring himself to kill (which, yes, in that context would make the Joker more heroic than Batman!). Only with his gassing of the news broadcast does the Joker move on to killing innocent people.
The Curb-Stomp Battle in the bell tower, where Batman gets thoroughly and humiliatingly destroyed by the third thug (who resembles a burly Ray Charles) while ballet music plays in the background. It's supposed to be powerful, intense and terrifying, but comes off being more unintentionally funny due the poor staging and choreography. And when you have Batman turning around a few seconds later and dealing out a major ass-whooping to the Joker, the Dark Knight's own difficulty taking down one thug looks even more ridiculous.
Also very Narm-worthy is a close up of Batman having a freaked out Oh, Crap! look on his face when the thug has him in a headlock just before he really gets down to business. It's not pretty... nor is it as frightening as it's meant to be. And it's hard to take the Ray Charles thug seriously when he's grunting and panting like a dog in heat.
Alfred leading Vicki into the Bat-Cave might be this as well.
In said Bat-Cave scene Vicki says to Bruce "I've loved you since I met you..." when their relationship seems based mostly on a one night stand. Seems Bruce must be great in bed...
The use of Prince songs was cringe-inducing enough at the time, and is now even worse as they instantly date the film every time they appear. What makes it worse is that Prince did write a song — "Dance With the Devil" — that more closely fits the mood of the movie and has dated quite well, but it was cut from both the movie and the tie-in album for being "too dark."
Narm Charm: As cheesy as the Prince songs are, there's something fitting when it comes to seeing the Joker dancing around to both "Trust" and "Partyman" like a maniac given his Psychopathic Manchild behavior.
No Problem with Licensed Games: Most games based on the movie, either on consoles or computers, were actually quite well received. The NES, Sega Genesis and Amiga versions in particular are remembered by many retro gamers.
Romantic Plot Tumor: The amount of time focused on Bruce's relationship with Vicki - who is also desired by Knox and the Joker - makes this subplot come across as this to some viewers.
"Seinfeld" Is Unfunny: The first film was unique at the time. Comic book movies, and there weren't that many of them then, had never been so darkly elaborate before. It was also by far the darkest take on Batman beyond the actual comics. But after both the DCAU take on the characters and the Christopher Nolan reboot proved to be exceptional adaptations in their own right, and the lingering bad aftertaste of Schumacher's sequels tainted the series' reputation, it's harder to appreciate the Burton films for what they were/are.
The opening scene where Keaton's Batman says, "I'm Batman"
The scene after Joker's acid bath where he goes to a plastic surgeon and the Joker asks for a mirror, and he, back to the viewer stares at it and belts out the first Evil Laugh. This was later homaged in The Simpsons and in other works.
Special Effect Failure: The matte painting of the Batsignal clearly moves and ripples in each shot it's in. It is, ostensibly, supposed to look like it's being projected onto moving clouds, but the rippling effect applied to the Signal does not remotely resemble the visible texture of the clouds.
Spotlight-Stealing Squad: Even people who like the film will admit that this is essentially "The Joker Movie, Also Featuring Batman". YMMV on whether or not this is a good thing.
Uncanny Valley: Ironically, the Joker looks farcreepier when he's wearing the skin-toned makeup to make himself look normal than when he's being his regular, clown-faced self.
What an Idiot!: The first of the Joker's three goons at the top of the cathedral tries to take Batman down with a bunch of back flipping jump knife kick attacks, but Batman calmly defeats him by just punching him in the crotch - as if such an over the top attack would work on Batman of all people.
The second of Joker's three goons at the top of the cathedral is a big guy who tries to jump down on him from a higher platform. And promptly falls through the floor before Batman even has time to turn around, since his weight is just too much for the old rotted wood to support when he lands. Also qualifies as a Funny Moment.
When Batman is fighting the third goon, the one who looks like Ray Charles (see Narm above), at one point he actually tries what the second goon tried to do him - Batman tries jumping onto the guy, and not even having the good sense try jumping him from behind. What happens? The third goon simply grabs Batman in mid air and throws him into a rotted wooden staircase. And then he kicks Batman's ass in the most unintentionally hilarious way imaginable.
The third goon himself engineers his own death right after he gets done kicking Batman's ass - after kneeing Batman in his crotch with enough force to send him into the bell and then down the tower shaft the goon is actually dumb enough to look down as if to make sure he's dead. And then Batman throws his legs around the goon's head, and for some strange reason the goon is suddenly too weak to pull Batman's legs off. Batman then very slowly pulls the goon forward, bangs his head into the bell - and the goon is actually whimpering like a little kid who just scraped his knee as he struggles to pull Batman's legs off - and then pulls him all the way down and sends him falling to his death. Granted, he had it coming...
The Joker himself during his brawl with Batman. The most glaring example is when the Joker tries to attack Batman by distracting him through spitting out fake chatter teeth. He takes the moment to try to strike Batman by surprise, but ends up hurting his fist when Batman promptly crushes it before he could strike.
WTH, Casting Agency?: Michael Keaton so thoroughly proved the naysayers wrong that, in hindsight, it's hard to remember just how bizarre casting a famously mild, unimposing comedic actor as a grim, Frank Miller-inspired version of Batman seemed at the time. Thousands of fans wrote letters to Warner Bros. protesting the choice before the movie's release, and Keaton himself initially thought that his being cast for the part meant that the film would be taking its cues from the TV series.
Cool as the Batsuit looks in the movie, it was so stiff that Michael Keaton could barely move. The first time he tried to turn his head he completely ripped the cowl in half, then he had to develop a movement style that didn't involve turning his head. To Keaton's credit, the lack of mobility wasn't terribly noticeable until the second Tim Burton film.
As Grant Morrison pointed out in Supergods, Vicki Vale wears so much makeup in some scenes she could pass as the Joker herself. This trait was shared by just about the entire female cast across both Tim Burton films (sans Selina Kyle during her Hollywood Homely phase).