I remember reading Peter Kay's first book in which he revealed the ending to this film, which whilst irritating me at the time (as it was a film I quite fancied), prepared me for this terrible ending.
It was a good film, it got better as it went along and was very chilling but the sad ending did spoil the film. Also, some images of people that died in the film were a bit too graphic for my liking, especially if you're tucking in to a bag of midget gems as I was.
The film lives up to it's description of thriller to an extent, as it keeps you interested through it's mystery but there isn't enough action. There needs to be another incident or two during the killings, where we either see one or there is a close call for one of the officers. It never really lived up to my expectations in that department but it was worth watching and, like I said, it's thrilling in a chilling way and it keeps you thinking.
But the sad ending and lack of action let it down, as well as the fact that you can't help but slightly dislike Morgan Freeman's character at the beginning for being a dark, miserable so and so. But he gets better as it goes along, like the film in general does so I'd say this is worth watching and is OK but not a classic.