Though noticeably inconsistent in its pacing, Friedkin's The Exorcist does deliver plentiful shock and tons of technical marvel, aptly revolutionizing the horror genre at its time.
My pacing concerns are as follows. Without the Wikipedia article or any of the prequels/sequels, it's hard for viewers to make sense of the introductory Iraq scene and its correlation to the following events in Georgetown. It was also somewhat off-putting that the film didn't have a singular "main character", but instead altered between the narratives of the mother (Ellen Bustryn), the priest (Jason Miller), and the exorcist (Von Sydow). Their respective performances, as well as Linda Blair's, were marvellous without a doubt, but the overall structuring of their stories wasn't the most cohesive.
But besides that, there's tons of things to praise (in addition to the splendid casting and acting).Veteran makeup artist Dick Smith did such a great job engineering the makeup of von Sydow and Blair! I didn't realize von Sydow was wearing makeup at all, and was mind-blown to see him so organically aged. Wikipedia goes into detail, but Friedkin pulled all the stops to make The Exorcist look and feel so convincing. The effects hold up even against today's CGI-made monsters.
All in all, it's easy to see why The Exorcist made its unprecedented impact in 1970s audiences worldwide.