Having not seen it all the way through since I was too young to really "get" it, I was surprised upon revisiting it to find that virtually everything I remembered about The Exorcist were the elements that are still too-frequently used to make fun of it: the projectile vomiting, the 360-degree head spin, the demonic obscenities spouted by Linda Blair, the instantly evocative "Tubular Bells" theme music. But these elements, in the context of the actual movie, are really fucking effective why else would people still bank on their power when writing jokes for shit like Scream or whatever? And for the record, "Tubular Bells" is heard only twice in the film, and for about 15 seconds total.
So, expect the unexpected. Even now. Even with everything you think is certainly ridiculous or dated about it. The Exorcist holds up in pretty much every way.
Though the pace is very slow, it is ideal for creating the slow-brewing creepiness factor and for setting up the explosive climax. Friedkin uses a lot of restraint in not showing much more than the briefest glimpses of what is to come, and some of the best scenes are the single-frame "subliminal" splices that show Satanic faces so quickly that you start getting scared purely out of reflex, like when you wake up at 4 in the morning to go pee, and in your half-asleep state believe yourself to see shadowy figures just beyond the corner of your eye.
Linda Blair is just astounding as Regan, playing the sweet side more sweetly than any child actor I can think of, and the possession scenes with a command that would take 40,000 Culkins to even nearly approach. It's a real sad thing that Blair was so good here as to negate the future career she probably richly deserved.
The prologue is a bit overlong, and some of the priestly dialogue scenes seem a bit overly serious. But the visual effects still hold up, and if there's anything that genuinely disappointed me about the film, it was only the sense of pop culture having cheapened it to whatever extent. But I suppose inspiring attempts at imitation is an inevitable side-effect of creating the truly inimitable.