So the question I have to ask is what the fuck do the public see in the film? Are they inured by the gore or the soap opera storytelling (admittedly the continuity is impressively convoluted).
But for me, each Saw movie is sort of like a retarded magic trick, I tune in each year to see how cleverly they've devised their latest twist ending. Frankly, I thought IV was the best, but you have to remember the details of Saw III for it to make any sense. I think people reacted badly to the level of brain activity required for it, and the resulting V was the worst yet: dull and straightforward.
I saw the first one prior to its release with James Wan (co-writer/director) and Leigh Whannell (co-writer/actor, Adam) in attendance, and they addressed the cheapness of Saw head-on, saying they just didn't have the time or budget to film cars on a road, nor did they have the footage available sometimes to pad out the runtime (photographs in the first movie is due to a lack of other footage to use).