When Saw became a hit out of nowhere in 2004 nobody expected it to become a successful franchise with numerous sequels. After all with its cheap 1.2 million budget you wouldn't think it would be possible for Saw to be the highest grossing franchise in horror history. Saw is labeled as horror but it's much more complex than that, there's a lot of psychology involved. For instance the main character John Kramer, known as Jigsaw because he removes a puzzle piece from his victims, is labeled as a serial killer but it goes deeper than that. Jigsaw chooses his victims very carefully, he selects persons because 1) they don't appreciate life or 2) they've done something really wrong. He is testing their will to live trough his 'games' which are traps that often necessitate the victims to lose a body part or to go to extremes. You see, Jigsaw's goal is not to kill but rather to have the survivors enjoy life; it's a therapy he made. Saw puts photographer Adam and Doctor Lawrence in a disuse industrial bathroom both with their ankle chained, I the plot is now known enough that I don't need to explain what happens next.
Saw became a phenomenon and in my opinion is one the best horror movie of the 2000s decade; it gave the horror genre a boost and inspired other movies. Whatever people may think about some of the sequels, the original one remains a great film and I think it's one of the best horror movies made.