Had "Madman" come out before "Friday the 13th" it would be considered one of the great classichs of the slasher genre. So it is just a very entertaining movie. Admittedly, the story, as other reviewers have pointed out, is not that original, maybe even silly, the acting is not great, you will probably laugh at the make-up of Madman Martz, and the music sounds like someone is just trying out the new synthesizer, but there are some great scares and a number of reasonably inventive kills. Don't expect too much gore, though. What "Madman" is lacking in blood, it more than makes up with its chilling atmosphere, courtesy of dense woods and the old Martz house.
Definitely one of the better 80's slasher films and worth to be added to a true horror film fan's collection. Watch it with the commentary track on - it's just hilarious!