The Exorcist

William Friedkin plays it completely straight and takes the theology seriously, which is why it still works when the imitators do not. A child is possessed, two priests are called, and the film spends its length making you believe in something you do not believe in.

It became the highest-grossing R-rated horror film for good reason: the craft is impeccable, the escalation is patient, and the practical effects still land. It caused genuine public panic and a decade of rip-offs.

Not exploitation, and the standard the whole occult cycle failed to reach.