This movie was a master-piece for its era. The movie's special effects were before their time. We were able to see never-before-seen scenes where Regan's head does a full 360 degree turn, sexually mutilates herself and vomits powerful streams.
If compared to movies of its time, the movie is good, but compared to what has been done since 1980, it is not amazing. The story moves along very slowly but the shocking scenes stay in your head for weeks.