Interesting you say that since Friday the 13th was exactly what you described Saw to be: mindless torture porn (in this case a body count flick) and a story line that isn't shy enough to repeat itself sequel after sequel, pretty much like Halloween (except part III) and A nightmare on Elm Street (it did have a novel concept, I'll give you that.) Plus, Saw had more character development than your typical slasher movie.
It did start to get ludicrous by the 4th movie, though. I mean with Jigsaw gone and his successor taking over, it seemed that the makers of the movie wanted to keep the series alive (much like older films).
So yeah, Saw began to rot after the 4th (with a little improvement on the 6th entry), but I still prefer this series over the older, hack-and-slash flicks.