By now everybody in the world has probably heard about the Manhunt 2 ban. The BBFC has refused to rate it in the UK and the game's been given an Adults Only rating in the US, meaning Sony and Nintendo won't go anywhere near it.
Of its decision the BBFC said, "Manhunt 2 is distinguishable from recent high-end video games by its unremitting bleakness and callousness of tone in an overall game context which constantly encourages visceral killing with exceptionally little alleviation or distancing." Basically you don't do anything apart from killing people all the time.