I haven't watched the movie in 15+ years, but I remember being really into it when it came out.

It's not the standard Disney animated "musical." It's been ragged on because it failed at the box office due to the perception that it was too scary for Disney's traditional audience; with it's undead hoards and whatnot. I'm guessing it's probably not as bad as the rap it gets, but Disney apparently has kept it guarded ever since.

Incidentally, it was the first animated Disney movie to NOT get a G rating.