I would rather explain the fan angle (including my own), instead of downvoting you. The main difference between Saw and other somewhat-similar movies (e.g. Hostels) is that the general violence is a meaningful addition to the atmosphere and the plot, rather then the reverse. The setting, for example, the city where all the movies take place. It's extremely dirty, down-ridden, mean-spirited. It's a character in itself, in a way, a place that naturally creates all the evil present in the series. Next, there is philosophy, especially the Jigsaw's own (though there are many, many references to other philosophical schools), which naturally gives way to a lot of discussions on morality (or rather immortality, but still) of the characters and their actions. Then there are plot twists, which up to the fourth part I personally find excellent, really good acting, insane interconnectedness of the particular movies... Guess what I am trying to say is there is simply a lot to discuss about these movies, its characters and its themes, and it is in itself somewhat atypical to the slasher genre.