The 4K version of The Exorcist looks incredible. The picture quality has been improved so much that you can see more detail than ever before, which really emphasizes how disturbing Regan’s possession is. Certain scenes now have brighter colors, and this adds to the already stressful feeling throughout the movie. Well-known parts, like when Father Merrin first appears in the streetlights and Regan's head spins around, feel much stronger because of these improvements. The film's indoor settings—from Regan’s dark bedroom to the uneasy moments where Father Karras questions himself—are now clearer, which makes the scary feeling even more complete.

Source on TMDB