Saw IV, is based on a psychopath named Jigsaw who punishes people for their wrong doings in the most extreme games. This is to teach them a lesson in understanding how damaging their actions have been, and forcing them to receive their karma. This is the forth Saw film in the franchise, and it continues from the first.
In our opinion they could have stopped the Saw films after the third one, instead of continuing it all. However, this film was done quite well.