This movie should have cult viewing status. It is wonderful in the way it slowly but surely cranks up the tension, and keeps the viewer rivetted to their seats. It is obviously a little dated, but so many modern horror movies could learn so much from the psychological terror that builds in this one, without relying on gratuitous gore.
Sadly this movie seems all but forgotten. A few reviewers here raise issues of whether it is cut or not (this is the full, uncut movie. It may be that scenes have been cropped, but if they have, few people will notice or care). Other than that there is not nearly enough discussion of how good this movie is.