Honestly... it surprised me. A lot. The dirty cop is the perfect example of why you never actually root (that much) for the characters (with Daniel being the only exception where you actually want him to live) since the movie shows you all the crap they did in their lifetime.
The formula was not enough. And it is kind of sad, and sadistic, to create entertainement like this. A good (bold) filmmaker would deconstruct things. Even if not to the extreme of Haneke's Funny Games. But as the series progresses, there seems to be a morality, a very stupid morality. And it's like the victims deserve to be punished. There's no patience for this. It seems like an excuse for the viewers' sadism.
the introduction to one of the most psychologically clever and twisted villians since Hannibal Lector. Seriously, i rewatch this film just for the dialogue scenes with Tobin Bell. The only let down is how stupid and emotionally driven, in contrast to Jigsaw, the victims are. But that's the point, you almost find yourself siding with the villian, which makes it all the more creepy.
...and then Darren Lynn Bousman comes along with a completely unrelated script that Lionsgate asks him to turn into "Saw 2," which unsurprisingly turns out to be the best film by far in the entire series. If this had been the original "Saw," the series' popularity would have made a lot more sense.