The film begins with a psychotic warden of a prison played by Dieter Laser, getting advice from his accountant played by Laurence R. Harvey. The warden spends a great deal of time torturing inmates and chewing scenery. His accountant suggests to him that the way to cut the costs will be to make a massive 500 person human centipede out of all the prisoners. After consulting with the director of the films, Tom Six, they find a way to make it so that prisoners can easily be removed and replaced in the centipede.
The clever thing about this movie is that it starts with the characters watching the previous films. It is familiar since the second movie begins in a similar fashion. Then the characters are introduced and anything clever about it goes right out the window. At first the warden, Bill Boss, is sort of amusing with how over-the-top Dieter Laser portrays him but it gets old incredibly fast. Laurence R. Harvey, is dressed up like a fat Hitler most of the film, which makes him look ridiculous.
The effects are not anything great. It is certainly a self-aware movie that wants to be funny but fails when it goes out of the way to attempt to gross the audience out. Scenes like boiling water boarding a prisoner, castrating a prisoner, or a dream sequence that involves prisoners cutting into the warden to make a new orifice to rape are purely there for shock value. After two previous movies of unpleasant exploitation this is not new or even shocking.
When it comes to a trilogy like this the mindset should be it to burn out instead of fade away. The casting of Bree Olson and Eric Roberts as minor characters is bizarre and yet forgettable. There is not a real reason to watch this movie unless you are super fan of this series or are an exploitation film fan. In which case, there are a lot better things that you can be watching instead of this.