It's only worth watching if you're not expecting a quality film.
My friends and I originally went to see it purely for the "shock factor" of all the greusome shit in it. If you're actually expecting a quality film with a well developed plot, avoid it, as it's shite.
However, it's a great movie to just pop in when you're drunk one night with some friends, since it's almost as funny as it is shocking
(the first 30 minutes are more or less softcore porn)