The Exorcist. Now 40 years later I decided to watch it again, thinking I'll wonder why it scared me so bad...Still scared the bejeebers outta me after all these years, especially when she crawled backwards down the stairs!!
My favourite horror film, bar none. Every single possession movie I watch is measured against this masterpiece.
I had a similar experience to you. I watched it first as a little kid with my sisters. Scared the living daylights out of me. I didn't watch it again until in my 20s. I wanted to see if it would still have the same effect on me. Stellar example of masculinity that I am, I watched it at home during the day. Living daylights scared, again. Bought the boxed set of all the DVDs some years back. I love this film to no end. Still, it is the one movie I continuously watch and even though I know what's coming with every frame, it still terrifies me.