I have been recommending this movie to everyone since I left the theater. This movie was the greatest horror film of my lifetime. I have always been a huge fan of the Halloween franchise, I enjoy all of Rob Zombie's B-rated horror films, I've seen all of the Friday the 13th movies, Nightmare on Elm St movies, Exorcist movies, Quarantine (one of the best - in the dark), The Exorcism of Emily Rose, etc etc etc...
Of my list, the Exorcist was the only movie that really stayed with me for longer than a few hours.
If you have any desire to test your wits and / or the staying power of a Horror film, this is the movie for you.