A series of murders, mostly on mob people, on holidays drive Harvey Dent crazier and crazier, ultimately becoming Two-Face. The comic's a long, slow burn, but has some great moments, including my favorite Thanksgiving meal; Batman's a monomaniacal jerk, but has compassion for some of his antagonists. The mobs really just own Gotham, and hunting down The Roman won't change anything, but it's the thought that counts.
The cartoon movies are a mixed bag. The male characters pretty much all look alike, sometimes with different facial hair; the artist really only has two models, hulking brute like Batman, Dent, Gordon, Falcone, or weedy little dudes like Joker, or nerdy Alberto Falcone. The female characters, too, are all perfect flapper types from a single model, distinguished only by haircut. The scenes are dark even for a Batman cartoon, so it's often hard to make out more details than rough outline.
Jensen Ackles is not a good Batman, he's whiny. Troy Baker as Joker is lame, but I don't like anyone but Mark Hamill for the role; he's especially perfect for it in The Killing Joke, and is supposedly "retired", but really they should've paid or done anything for him to come back. The rest of the voice cast are adequate, Billy Burke's Gordon and Naya Rivera's Catwoman are even pretty good. Josh Duhamel is too growly to be professional lawyer Harvey Dent, and too clean to be cackling, half-mad Two-Face.
The movie does give hints about who Holiday is throughout, but it's not laid out as well as in the comic, there has to be a long, slowly-delivered monologue at the end.
Still, here's your Halloween Batman, which is the best seasonal Batman.