I've given this "opera for TV" five stars, but I urge you seriously not to watch it. It's extraordinarily painful, and enough pain will come your way without the help of music and cinematography. Still, anything that disturbs me so strongly must be potent art in its way.
This is a depiction of dementia (as in possession by demons), sado-masochism, flagellation, torture, and burning alive at the stake. It could, I suppose, be perceived as an indictment of religious depravity and the corruption of organized faith. It is certainly depraved, but I take it to be more a portrayal of the torment of religious doubt, the hideous psychological self-hatred innate in a religion of guilt and redemption. The composer, Krzysztof Penderecki, if I remember correctly, went through a religious crisis and "conversion" not long after writing this opera. The visual and verbal impact of this film are much more powerful than the music, if that matters to you. I defy you to remember a musical passage, or to forget the image of the gleeful torturers.
It was filmed in 1969. I would have said, before watching it, that the world has become a more violent and tormented place since then, but The Devils of Loudun has reminded me of the dark and twisted anxiety many of us lived through in the era of nuclear nightmares, Vietnam, the Zodiac and the Zebra killers, etc. I'm glad I survived. I'm glad I have a few flower boxes to water and cultivate. I'm glad I'm not oppressed and perverted by any demons of religious dread. It's good to look at the hills and see millions of years of gentle erosion, to play with my son and feel proud to contain the whole sublime history of evolution in our DNA, to look at the sky and see only stars, not devils nor gods.
Above all, dear reader, you are not required to suffer through Penderecki's obsession; some art is optional. There are plenty of other options.