The 1980s was a boom period for fantasy cinema. Everyone was hoping they'd find the next Star Wars and pretty much always failed, but at least succeeded in producing a lot of cult classics. Now, there's two types of cult classics. There's the genuinely brilliant films that just never managed to find a wider audience, and then there's the genuinely bad films that many enjoy because of how entertainingly bad they are.
I'm not sure which group I would put The Black Cauldron in.