Perhaps there is little point in writing a negative review of a movie that not many people will see. Also, I walked out at the intermission, so I am only half-qualified to write (although I have been told that it gets worse in the second half). Still, given that the few IMDb reviews are much more positive than the average IMDb rating, it might be useful to have a review that represents the opposite side.
So what is wrong with this movie? Two things. First, as other reviewers mentioned, the writers threw into it everything that came into their minds, aiming mostly for shock value, at the price of flushing plot and character development down the toilet. Second, the setting is very bleak and gritty. One could object that Kurosawa's samurai movies, or Roman Polanski's Macbeth, are also bleak and gritty, but they have great plots, great characters, and manage to be uplifting, which is more than can be said for this movie. Maybe it is a realistic portrait of the most depressed areas of Dublin, as the Irish reviewers say. However, it is not a side of Ireland that many foreigners will like to see. If there were some insight to be gained into human nature, it would still be worth seeing an unpleasant movie, but I do not feel that this is the case here.
Update 2008.03.27: I decided that it is not fair to give the minimum rating to a movie which does not disappoint. I could not be disappointed by this movie because I did not know what to expect, so my rating is slightly increased.