Try to see the version that was re-released in 2000 that added some scenes that were cut from the original 1973 release. (The "spider crawl" down the stairs is the first that comes to mind, but there are others as well). It also added some footage to the ending, but I think the original ending was more effective.
Also the theme music("Tubular Bells") is perfect for that movie. It still gives me chills.
Lots of <<insert vomiting smiley face here>>
My wife is Catholic and I took her to see it and it made her a little uncomfortable, but it is a great story. It has some good underlying themes. It is just not a shocking horror flick with a lot of green vomit.
I'd recommend the book too.