I enjoy Saw largely because it's one of the few movies that doesn't seem to be afraid to show horrible, and nasty things without resorting to making things too dark, jumping around, or simply implying the violence and such. Saw for the most part does NOT pull punches with the gore and violence. Don't misunderstand what I am saying here though, I am not saying Gore and "splatterpunk" nessicarly make a movie horryfying.
To me (someone who grew up with the "Nightmare On Elm Street" franchise) this is a big thing, and no matter how badly the script blows I am going to support Saw as long as they continue to not pull the punches.
Oh sure I would LIKE to see *other* movies take this kind of approach and do something new (after six movies, and apparently 2 more on the way), but it doesn't seem to be happening.
See, all too often "cereberal" and "psychological" horror is basically an excuse for "we didn't want to slot off the censors". In many cases, to me, it's obvious when they are pulling punches to avoid offending sensibilities. Saw takes the opposite approach. You don't NEED gore, but when it should be there, they should include it, and they shouldn't be writing horror movies just to get around it.
To me the "perfect" horror movie is one that both includes a novel story (or at least well told stereotypical one), along with not pulling the punches. When the bad stuff happens I want it to be there in all of it's sexy, bloody glory.
I tout "Nightmare On Elm Street" and it's sequels as the best series of all time for horror movies because to be entirely honest Freddy Kreugar was an original idea when it came out. Also when he killed people in these surreal dreamscapes, they did not pull punches. Indeed for the time these movies were made they were using some very awesome special FX. Of course I also suspect that their success was partially rooted in the fact that they had guys like Johnny Depp, and Laurence Fishbourne in them before they were famous (vague shades of "The Rocky Horror Picture Show").
Take a fairly good, well written/designed story like "Drag Me To Hell", or "Paranormal Activity" and then turn the whack jobs who come up with ideas for SAW loose on it.
Right now we have all the makings of great horror movies/franchises but we're too much into an either-or situation.
Plus, as I said, I support SAW more than any of the other cereberal stuff because SAW is uncomprimising, and becoming contreversial hasn't exactly gotten them to chill out.