The Devils (1971)...by the ever incorrigible Ken Russell.
It's difficult to put into words exactly what makes Russell's films so...is "on-putting" a word? It should be: it's basically the same as "off-putting", insofar as that there's something bizarre and disconcerting experienced, except that it's interesting and entertaining instead of being unpleasant or tiresome as you would rightfully expect given the content. The man has this inexplicable superpower of making films that don't really have any right to be good...exactly that. I would say this is his best film of the ones I've watched, and I was rather enthralled by both characters, story, themes, and performances, though I think I still ultimately liked The Boyfriend a little more for subjective reasons. The Exorcist is widely remembered as one of the best films of all time while The Devils was heavily censored and disavowed by the media: it perhaps seems a strange difference in reactions, given how many similarities you might notice between the two and that they were released at close to the same time (1971 vs. 1973). I suppose The Devils has a more...dual nature, in that the audience has to grapple with the fact that it walks a very fine line in being comedic, nearly parodical, in how outrageous (though never unintelligible) it gets - in grave contrast to its all too real messaging on the harrowing and dangerous intersection of politics, religion, and human nature, among a number of other things. I could see that offending many political and religious sensibilities where The Exorcist didn't, as The Exorcist always played it straight, always treated the religious and supernatural elements very seriously while keeping any commentary it might have on them quiet enough, while The Devils most certainly did not.
On the other hand, I wouldn't dream of The Devils giving up on its funnier, more sociopolitical side if it meant the film forsaking the scene where a carefree and whimsical King Louis XIII lounges around in the raving throng of "demonically possessed" nuns. Who else is going to dispel the demons from all of them with an ancient vial of Jesus' blood inside of a relic container before impishly revealing that the box was in fact completely empty, causing the possessions to resume as if they hadn't ever paused? I was quite saddened the king didn't show up at either the trial or the stake burning, but I suppose His Majesty's delightful presence there would've rather undercut the film, so it was probably all for the best.