The Midnight Meat Train

A horror short story by Clive Barker, later adapted into a Slasher Movie by Ryuhei Kitamura. In it, Leon Kauffman, a photographer, is attempting to find the "real" New York City. He begins to delve into the city's inner "darkness", and while there, discovers a monstrous serial killer roaming the subways -- and then he meets his boss.

Tropes used in The Midnight Meat Train include:

Adaptation Expansion: The short story takes place over a very short period of time: Leon complains about the city in narration, bumps into and spills coffee on someone (who turns out to be the killer), reads about the "Subway Slasher", and the next day is trapped in a subway car with him -- cue climax. The movie pads out the story to build suspense and give Leon more character development.
An Aesop: Debatable, but it certainly seems to be influenced by Barker's vegetarianism, and dislike for New York City. You can easily enjoy it without caring about either of these things, though.
Ancient Conspiracy
And Then John Was a Zombie: Leon.
Big No: Two right after each other, one where Leon sees Maya on the train, and one where she sees the train car full of corpses.
Bittersweet Ending: The Butcher is defeated! Oh, but, Maya's dead, Leon is the new butcher, and this is all much bigger and much scarier than you can ever understand. You work for us, now.
Blood From the Mouth: Mahogany.
Body Horror: Mahogany. He cuts weird, fleshy nodules that look like barnacles off of himself and keeps them in jars filled with some kind of fluid. It's implied that this is some kind of deterioration from being The Butcher. From the number of jars and the almost routine way he does it without feeling any pain, he's been doing it for a while.
Brick Joke: The pre-credits scene in the film shows a subway murder by a man in a suit that we assume is Mahogany. After what happens to Leon, just before the end of the movie, we see it again, and realize that it is, of course, Leon, not Mahogany.
The Cameo: The Japanese supermodel who Leon rescues from some thugs and Mahogany kills is named NorA, and was in Kitamura's previous (and final one made in Japan, as of this writing) movie, LoveDeath.
Death Glare: Leon at the art gallery staring at the picture of Mahogany in the meat-packing plant, and then the two of them at each other just before the final fight scene.
Eldritch Abomination: The Elders. And in the short story, the thing the Elders appease when not eating people fillets.
Face Revealing Turn: See Brick Joke, above.
Gorn: Oh hell yes. The murders, naturally, but also a long and detailed scene showing Mahogany stripping the corpses. That is, cutting off their hair, removing their teeth, eyes, and nails, and hanging them on hooks. Remember that this is also, essentially, what actual butchers do to actual dead animals.
He Who Fights Monsters
High-Pressure Blood.
Hidden Agenda Villain: Mahogany's motivation for not killing Leon right away, it would seem.
I'm a Humanitarian: Anyone who works for the Elders, apparently.
Invisible Advertising: See Screwed by the Network.
Legacy Character: The Butcher.
Ludicrous Gibs.
Man of Wealth and Taste: The Butcher.
Mind Screw: Not really, but given the vast amount of backstory that must exist but is left unexplained, it can be fairly confusing.
Mr. Exposition: The conductor, if only because he's the only one who explains anything.
New York Subway: You guessed it.
Police Are Useless: ...because they're in on it!
POV Cam: Several times, from the victim's point of view. Including post-decapitation once.
Pre-Ass-Kicking One-Liner (and Crowning Moment of Awesome): "I've got a train to catch."
Rain of Blood.
Room Full of Crazy: Once Leon becomes obsessed with "the Butcher".
Screwed by the Network: The movie was utterly fucked over after Lion's Gate came under new management, and the new CEO deliberately killed off all the projects his predecessor was championing. After repeated attempts to make the movie "appeal to a broader audience" were fiercely rebuffed by Barker and Kitamura, they decided to technically honor their contract and release the movie in 150 bargain theaters in the American Southwest. There was a campaign by Bloody-Disgusting and a few other horror sites to buy as many tickets as possible to make a point, but it was too little, too late.
Sinister Subway: Well, duh.
Spoiler Title: The last track on the soundtrack CD is called "Leon The Butcher".
Subways Suck: Much worse than usual, but also played with. During Mahogany's second kill scene, the husband is busy reassuring his wife that the subway is perfectly safe, and that those stories are all outdated.
Technically a Smile: The wicked little grin Mahogany gives Leon on the train.
Town with a Dark Secret: New York City!