The Exorcist (1973) is a good movie. First, remember it is from 1973. The special effects weren’t that evolved. Thus, a lot of them are just make up. Nevertheless, you can get some great views, like rotating heads, levitation and some other. The story is mostly what you would expect for the title. The main drawback is that we do not get a proper exorcism working. The devil disappears by other means (check the movie to understand). Also, there are some minutes from he beginning of the movie that aren’t relevant. I know they connect with the exorcist, but in fact they do not bring anything new to the story. With those scenes, the story could be made better and more interesting. But probably the director noticed the movie was getting too big, and just decided to cut the story. I just can say I think the end could be a lot better.
Also interesting is to read about the actress who made the girl character. She was almost nominated to an Oscar, but then they noticed she used some stunts and a dubbed version. So, if you want an Oscar, try to make it real.