I love this film.
And it is an horror film. Besides some LOL and some ROFL here and there, some scenes are scarier than the most part of horror films from Hollywood nowadays. For example can be a bit shocking the scene in which he see something is growing inside him, with the eyes emerging from his shoulder... or when he mutilates himself with the chainsaw in the prologue.

But I'm sure it's rated R because of the "sex scene" :D