SURPRISED! This was actually a pretty well-made movie!
From the title and notoriety, I was expecting this to be 70s shlock of the worst kind - something akin to the goofball nature of the original LAST HOUSE ON THE LEFT.
I was surprised to find competent acting, professional staging and camera work, and a compelling story, albeit simple. I thought the rape scene was handled in a way to make the viewer really hate the rapists, and never once to entertain or titillate the audience. I thought the revenge sequences were appropriate without being over-the-top and disturbing (as the remake appears to be).
For a basic rape/revenge film, I found this much more watchable than I had anticipated.