I have just finished watching this film (bought at a great price from Amazon) and was very, very impressed.
I do wonder whether some of the reviewers here watched something else - do give this one a try if you have a couple of hours to spare. You may like it, you may not but you will never know if you don't try it.
One reviewer mentioned that it is the viewer who plays the most important role, as it is our interpretation of the violence which makes the film really work. How can you be pleased when you see someone blown away? - somehow I was, which is disturbing.
One of my favourite films this year (but my husband just went 'yeah it was OK' so it won't be for everybody).