Aside from The Prey, this is probably the most hated film on my list. It's definitely a "sleeper slasher", I can understand why some people don't like it. It has a small body count(but effective), there are long scenes where not much is going on, and the acting could have been better. What people fail to realize is that Unhinged is more atmospheric than most horror films from the 80's, and the shocking "twist" ending was ripped off by a much better known film.
The story involves 3 young ladies who are travelling to a jazz festival, when they encounter bad weather. Their car ends up in a ditch, and one of the girls is hurt. A man finds them and takes them to a huge, scary mansion inhabited by a crazy old lady and her spinster daughter. They agree to put them up, but there is no phone for them to call for help(imagine that?). After a day or two in the house, one of the girls decides to walk a few miles through the woods to the nearest village for help. Needless to say, she doesn't make it that far, she is attacked in the woods by a scythe wielding maniac. Back at the house, one of the girls starts hearing a mans voice at night, making sounds which could be accompanied by masturbation. She even gets a glimpse of this man out of the window, and the spinster tells her it's her retarded brother that is forced to live outside, because the Mother has a deep hatred for men. Then a second girl is murdered, and it's left up to the last girl to solve the mystery, and it's definitely not what you think it is. The twist ending is the best part of Unhinged, it's definitely a WTF moment.
You can get Unhinged on DVD for relatively cheap, and if you don't have to have a huge body count to enjoy atmospheric horror, check it out. It is a bit dramatic though.