Author Appeal: Catwoman starts out as a prostitute. Yup, it's a Frank Miller comic, alright. Distressingly, Holly is also one, and she's only thirteen, if that.
This is one of the few parts of the book that has NOT remained in continuity, and was made so almost immediately. However, retcon over retcon has actually led it to be the foundation of her post-Crisis character in certain ways.
Ax-Crazy: Branden and the GCPD SWAT team. They once put down a riot in Gotham's Not-Central-Park. Didn't even leave the statues standing. Their SOP seems to be: kill everything with fire.
Batman's speech while he's "convincing" Skeevers to testify against Detective Flass.
Batman: You can never escape me. Bullets don't harm me. Nothing harms me. But I know pain. I know pain. Sometimes I share it... With someone like you.
Batman: Ladies. Gentlemen. You have eaten well. You've eaten Gotham's wealth. Its spirit. Your feast is nearly over. From this moment on - none of you are safe.
Gordon deserves special mention as well:
Gordon (internal monologue): He's had Green Beret training. It's been a while since I had to take out a Green Beret. *tosses Flass a baseball bat* Figure I should give him a handicap.
Bad Cop/Incompetent Cop: At the start of the story, Gotham Police Department is made entirely of these, from the Commissioner on down. Lieutenant Gordon and his team seem to be the only cops who are doing what they're supposed to be doing...
Batter Up: Gordon gets ambushed by a group of dirty cops who beat him to a pulp with baseball bats. Later on, Gordon confronts Flass with a bat of his own... but instead of attacking him with it, he tosses it to him and kicks his ass bare handed.
Dark-Skinned Blonde: The girl hanging all over Bruce's arm when Gordon comes calling at the manor in chapter four.
Demoted to Extra: In the animated adaptation, Dent is only seen and mentioned once when Gordon investigates him on the belief he is Batman. In the comic he was one of the main three that took down the corrupt network (aside from Batman and Gordon) but he was either not mentioned or his involvement was given to Gordon (such as the reason IA was going after Flass was Dent's doing in the comic but Gordon's in the film and the reason Skeeter was given parole was Dent's doing so Batman could interrogate him). This was most likely due to focus more on Gordon and Batman's beginnings.
Dirty Cop: The Gotham City Police Department is swimming with them, although Detective Flass is the most obvious example.
Dude, Where's My Reward?: Catwoman's first heist results in Batman getting the credit. Her second heist does net her credit... as Batman's assistant.
First Name Basis: Gordon realizes his affair is getting too serious when he starts calling her Sarah instead of Essen.
Follow the Leader: This storyline was so successful, it kicked off the various "Year One" storylines in DC, and Marvel.
In a poor attempt to act affable, Flass gets rid of a frail Buddhist monk who's nagging Gordon for donations by picking up the monk by the collar and tossing him aside like a rag-doll. He also beats up a kid allegedly to disarm him of a switchblade. It's a comb.
Not to mention Loeb's decision to try to corral Batman... by firebombing a building full of winos.
There also a near-literal example, combined with a Pet the Dog for Batman. SWAT agent Pratt gets annoyed and tries to shoot the cat used as a Cat Scare. Not much later, Batman punches him through a wall over it.
The Mafia: Since this is Batman's first year out, none of his iconic Rogues Gallery has shown up yet. Thus, these guys take the role of the bad guys.
Mythology Gag: The title of the first chapter: "Who I Am and How I Came to Be" is a reference to the title of the original Batman origin story: "The Legend of the Batman: Who He Is and How He Came to Be".
Mama Bear: When a pimp is abusing Holly Bruce tries to intervene. When he attacks the pimp Holly stabs him with a knife. When Bruce knocks her aside Selina leaps from the hotel room to kick his ass.
Painting the Medium: Gordon's narration has a printed font on a yellow background, while Batman's is cursive on white.
Panty Shot: Not shown to the audience, but during Gordon's visit to Bruce Wayne, Bruce sat crossing his legs while in his robes, prompting Barbara to avert her eyes.
Le Parkour: Bruce Wayne relies on it while pursuing some kidnappers across the city, during the day.
Period Piece: Not for the original mini-series, which was written in the mid-80s, but for the animated adaptation which is incredibly faithful; it's been more than a generation since Hare Krishnas offered people literature at train stations or airports, for example.
Post-Crisis: This is Batman's origin told for the Post-Crisis DCU, removing the weirder bits from the earlier eras.
Pretty in Mink: Martha Wayne wears a white fur coat (it's when she gets shot, but otherwise counts).
Recycled IN SPACE!: Gordon's part in the story plays like Serpico, a sole honest cop trying to clean up a corrupt department, but with Batman.
Sequel Hook: The last few frames is of Gordon revealing he received a letter from a guy calling himself "The Joker" who is threatening to poison Gotham's water supply.
Smoking Is Cool: Ironically, the corrupt Detective Flass and Commissioner Loeb seem to be the only cops that don't smoke.
Spotlight-Stealing Squad: Though a well loved series, one common complaint is that the book feels more like "Gordon: Year One" than "Batman: Year One". Indeed, his story makes up the bulk of the comic, and he certainly steals the show. That said, his story is hardly bad by any means.
Supporting Protagonist: Especially in the film, Jim Gordon comes across as the true main character of the story, even being the first in the end credits, than the title character who is shown more as a supporting character.
Super Hero Origin: The point of the story is to show off the origins of Batman, Gordon, and Catwoman, although the last was quickly retconned.
It was eventually re-retconned back though.
Switching P.O.V.: The arrival of Gordon and Bruce to Gotham, in the begining of the story. Gordon arrives in train, and thinks he should have taken a plane... and Bruce arrives in plane, and thinks he should have taken the train.
Talkative Loon: Albert Blume, a paranoid schizophrenic who holds three children hostage in chapter two.
Blume:Spider nasty don't noise it—no lunch. No lunch.
To Be Lawful or Good: Gordon struggles with the fact that he should be pursuing the obviously righteous Batman, who is, on paper, a criminal.
Holly: Selina! Things are blowing up near the park!
Selina: Maybe Branden's cornered a jaywalker.
Unreliable Voiceover: In chapter two, Flass is narrating the story while Batman attacks him for taking money from drug dealers. Naturally, what he says and what happens are polar opposites. When Gordon beats him up earlier in Chapter 1, he thinks that said cop will doubtless make up a story about twenty attackers and never admit the truth.
Ungrateful Bastard: After Bruce protects Holly from her violent pimp, she stabs Bruce in the leg.
Verbal Tic: Holly tends to whinily emphasize single syllables.
Commissioner Loeb also has a habit of answering his own rhetorical questions and reinforcing his own statements, yes he does.
What Could Possibly Go Wrong?: Bruce's first night home to Gotham, he patrols the streets "just for recon". It quickly turns into an epic screw-up where the prostitutes he thinks he's protecting attack him, the cops shoot him without question, and he nearly bleeds to death.
But it teaches him that he needs to instill fear into the hearts of criminals, who are a cowardly and superstitious lot...
And then his first foray as Batman - stopping a trio of burglars - he nearly screws that up as well (one very nearly fell to his death). Then again, this is an origin story: He has to start learning how to be The Batman...
It culminates in his saving an old lady from an oncoming truck. This leads him to get trapped in an abandoned building where he only narrowly manages to escape. After that Batman decides it's time to stop screwing up.
Would Hit a Girl: Bruce shows no hesitance in laying punches on Selena when she attacks him.
Your Cheating Heart: Gordon cheats on his wife Barbara with his partner, Det. Sarah Essen. Both know it's wrong, so Sarah requests a transfer to another city, and Jim eventually confesses to Barbara, vowing to work on their relationship. Also, Commissioner Loeb tries to blackmail Jim into "playing nice" by showing him pictures of the affair and later calling Barbara to tell on him. (By then, Jim has confessed, and Barbara quickly blows them off. This results in Loeb taking drastic measures.).
Adaptation Expansion: The film expands or completely adds a few scenes and makes things the comic left subtle a bit more obvious. The biggest example is a scene demonstrating that the girl Bruce had over during the Gordons' visit was simply The Beard working for $5000.
Creative Closing Credits: The first part of the film's credits shows off panels from the newsprint version of the comic.
Villain-by-Proxy Fallacy: Bruce is turned off of studying the law when he learns about Accessory/Felony Murder laws, specifically a getaway-car driver being judged equally guilty of murder if his partner kills someone during a bank robbery even though the driver wasn't even in the bank and doesn't know it happened.