Neither Bloody Nor Manic but enjoyable anyway
I got this on the Drive-In Cult Classics collection, and the first time I watched it I was let down that it wasn't as much of a horror film as it presented itself to be. But I've since watched a few times without those expectations, and it's a real pleasure for those who enjoy unintentional hilarity. The main title is classic. The blackmailer and his poorly pinned tie and sudden shifts of delivery - wait for the line "No, I am not crazy, thank you!" All the while Peter Carpenter is oddly leaning back and otherwise striking ludicrously unnatural poses. The laughable attempts at Bergman blocking/detached line delivery. And if you do find yourself getting bored, wait another 90 seconds and a woman will be undressing again.
It is definitely not good horror, or good film making, but if you enjoy low budget 70s clunkiness, this is fairly entertaining.