I personally have always looked at The Nightmare Before Christmas as much more of a Halloween film than a Christmas one. In part this is because the film is full of skeletons, ghosts, and ghouls-- including the protagonist of Jack Skelleton, a resident of Halloweentown-- but in larger part it is because it is a Tim Burton film, and he is known for dark and offbeat design.
The Nightmare Before Christmas is a musical stop-motion animated film that all started with a poem by Tim Burton. Jack Skelleton decides he is bored with the same old-same old of Halloween and decides to bring Christmas to his town. Unfortunately, things get complicated when the other townspeople don't fully understand the concept and keep comparing it to the former holiday. He adopts a new persona, that of "Sandy Claus," and has some townschildren kidnap the real Santa so he can be the one to deliver the presents. Santa gets dropped off with a gambling boogeyman, though, and it is up to Jack and his ghost-dog-reindeer Zero to save the day.
Though some studio execs worried in its initial release that The Nightmare Before Christmas would be too scary for children, the film has won over generations and generations-- from the slightly cynical Christmas purists (like me!) to the little ones with visions of gingerbread men dancing in their heads. Every year at Disneyland, those fans line up around the park to see the Haunted Mansion all done up for the "thirteen days of Christmas," just like in the movie!