The tyranist's thoughts
Before seeing this movie, I had heard both good and bad things about it, but almost everyone mentioned it as the debut of a very young Brooke Shields. Up front, you should know that yes, she is in it. But you should also be told that it isn't for very long. Sorry if that gives something away.
I would call this a prototypical slasher flick simply because of its age. The problem is that I can't really think of much that it influenced although I'm sure that there is something. Many will say that it has strong religious overtones. It doesn't. Instead, it is simply set in a religious environment, kind of like Prom Night 4: Deliver Us from Evil.
So a little girl is killed just before her first communion. Everyone but the girl's mother and father suspect her sister at once seeing as how the sister is more than a little deranged anyway. There are more attacks and murders and they finally discover for sure the real killer. Pretty standard fare if it was made several years later.
Personally, there were some scary, creepy moments that were mostly toward the beginning of the movie. The killer was actually pretty cool in that slicker and mask. There is a point where the tension disappears, however, and the movie plummets back into mediocrity. Since this predates most slashers, it lacks many of the elements that keep us watching them and therefore fails. If this had been made perhaps ten years later, I'm sure it would have been a better movie.