It's actually become something of a cliche for horror fans to prefer The Exorcist III (1990) to the original. I'm not here to weigh the merits of one versus the other, although I will say I've seen The Exorcist once or twice while I've seen its second sequel much more than that. If the original is an exercise in physical, emotionally grueling terror, then The Exorcist III is an intellectual challenge of the psyche. Whereas the original played graphic violence and shocking imagery, the third is built more on suggestion and ideas.
George C. Scott plays Detective Bill Kinderman, whom you might remember as a supporting character in the original played by Lee J. Cobb. Kinderman is investigating a series of murders committed in the style of the Gemini Killer (Brad Dourif), a psychotic murderer put to death in the electric chair fifteen years ago. Soon, a patient in a mental hospital's disturbed ward awakens out of a 15-year coma claiming to be the Gemini. Curiously, he bears a striking resemblance to Kinderman's friend Father Damien Karras (Jason Miller), a Jesuit priest killed performing the first film's exorcism.
It's really strange to consider the original is the one most remembered by mainstream pop culture. When you think about it, the original featured pea-soup projectile vomiting, spinning heads, and the infamous Crucifix bit, graphic elements you'd expect to find in an exploitation horror film (which you could argue The Exorcist is). Watching that little girl and those around her experience what they do is a grueling visceral experience and really puts you through the wringer. The Exorcist III, while not shying away from disturbing material, is more restrained. The violence is implied, the script dialogue heavy and concentrated on heady philosophical and spiritual issues, and there are crowd-pleasing cameos (such as Fabio and Patrick Ewing as an angels) and quirky humor that have been embraced by genre fans. It's a curious audience inverse, and I'm not sure why.
That paragraph above illustrates a key mantra for the film: those expecting the shock tactics of the original will be disappointed. Director William Peter Blatty (adapting his own novel Legion) keeps the horror on an intellectual level. The suggested ideas are what's frightening because they mess with your head.
The Gemini is a fascinating character. He's clearly insane, but he quotes John Donne, praises Shakespeare, and apparently is a medical expert, judging from his knowledge of tranquillizers and blood, uh, letting. I guess he's a perversion of human knowledge, susceptible to the devil and wanting to defy his father (both his biological father, whom he killed, and God). What's strangely effective is we only see him in the isolation cell, restrained in a straight jacket. Blatty films him in mostly shadow, his seemingly disembodied head floating in darkness and madness.
Meanwhile, Kinderman is a man who has lost faith, not just in God but the world. He's an officer who has seen every ghastly violent act possibly in the line of duty, and as he explains to his friend Father Dyer (Ed Flanders), he can't accept a god that would blindly allow all this happen. The people he encounters don't inspire much hope: priests without much guidance, a corrupt psychiatrist more nervous than his patients, and a hospital administrator more concerned about procedure than stopping a serial killer. People and setting of comfort do not offer sanctuary.
Blatty reinforces this by defacing religious, specifically Christ, iconography. The first victim is a young boy who is not only crucified on a pair of oars, he is decapitated, and his head is replaced with a statue of Jesus' head. Priests fall victim to the killer, and a nurse's body is stuffed with Rosaries. Churches are violated, and hospital rooms with crosses on the walls become crime scenes. This accumulation of violation creates an atmosphere of unease and disorder.
The ultimate violation occurs in the nature of the killer SPOILER! The demon cast out in the exorcism allowed the spirit of the Gemini to enter the body of Karras to continue his reign of terror. The image of such a holy and righteous man being used to spread death is no doubt the most despairing message possible for the faithful. END SPOILER
Scott, on one hand, channels General Patton in a few scenes. He really can pull off anger, but he also is vulnerable and wounded. Note the scene in which he snaps at the hospital administrator and then immediately fights back tears. Matching him in fury is Dourif, raving gleefully the joy he takes in killing while being able to ominously ponder and quietly explain how he commits the murders. When he stares straight at the camera and speaks, it's unsettling.
Every review of The Exorcist III must mention the ending and the shoehorned climax involving an exorcism, which the studio insisted on lest the title be misleading (or they could have let Blatty call it Legion like he wanted). What was a quiet, subtle film becomes a full-blown special effects extravaganza with fire, snakes, lightning, and the earth opening up. Considering how unnecessary it is, it's reasonably well done, and Nicol Williamson as Father Morning is a solid bedrock of faith and authority.
So that's The Exorcist III, an intellectual exercise and quiet, unsung masterpiece of the genre. It's certainly different from the original and effective in its own right. Who cares which is better?