The Human Centipede 2 adds little to the established story from the first film. It stands on it's own as it tells the story of an obsessed fan of the original. However, this movie lacks the depraved humor of the first and offers no character development at all. We are thrown in to a new "real world" scenario with a whole new batch of grotesque characters and nauseating sequences of flagrant violence directed towards all forms of human life. I didn't find the film quite as upsetting as A Serbian Film, but it's still a stomach turner.
Years ago, the phrase "torture porn" was coined with the advent of films like Saw and Hostel. The Human Centipede 2 moves far beyond the borders of that overused term. This is unfiltered brutality that truly pushes the limits of what I will stomach in a movie.
I would suggest seeing it but know what you're getting yourself in to.