This is the only movie that has ever given me nightmares.
Just to put that statement in perspective, I have seen HUNDREDS of horror movies, and this is the only one to terrify me so bad it affected my unconscious mind!
Speaking just about the technical parts, the direction is great, the acting is miles above what you'll see in 95% of horror movies, and the music is creepy as hell.
I loved how it made the villain a "Dark God", instead of just some generic demon. It puts a distinctly Lovecraftian spin on a horror film staple.
All in all, a great film.
Just don't watch it alone.
Or at night.
trust me on this.