Exorcist was for me a great read but a tough re-read. I don't understand people who say it is devoid of humor; Blatty started out as a comedy writer, and there are a lot of jokes in it, especially involving the Kinderman character.

Another great book in a similar vein, one that predates The Exorcist, is "The Case Against Satan" by Ray Russell. I would find it hard to believe that Blatty never read it.