Saw is a psycho-thriller in the vein of “Se7en” or “Silence of the Lambs”. It is able to stand on its own, though. A serial killer who calls himself “Jigsaw” puts people in carefully controlled situations in which they (in theory) have a way to survive; these situations usually have a personal connection to person being tortured. These games get more and more elaborate until there are multiple persons involved, all fighting for their way out of a death trap — at the cost of others.
The film is truly scary and horrific, and the way the plot turns is unpredictable, but not too far-fetched. In retrospect, I am not entirely convinced that the timeline of events holds up to scrutinity, but that thought never has time to come to the surface while actually watching “Saw”. Recommended.