Additionally I checked out "SAW IV", which from the off I felt was unnecessary. To be honest it was tied up nicely at the end of the third film, but they've found a way to keep it all going (albeit a bit of a naff one, just find a new apprentice in pretty much the same way as before).
I am a huge fan of the original "SAW", it was fresh, unique and the ending left my jaw on the floor (although not hacked off in a pool of blood thankfully). The follow-up however, I didn't really like. The premise wasn't as good, the characters were cut and paste bastards - whore, junkie, whiny little bitch teenager, panicky white collar worker, school-of-hard-knocks black guy and so forth. No wonder it wasn't as good, it was based on Bousman's own script for a completely different film, and James Wan did not have a hand in the script (only Leigh Whannel). However, those two chaps did have their hands in the script for "SAW III", which produced a much better film than "SAW II" I feel, the ciclical nature of the film - treading alternate and unseen angles of plot from the first two films - was what I enjoyed most ... and yes, rotted-pig-slush-device-thing was the grossest thing I've seen for a long time.
As for "SAW IV", with damn near everybody from the previous three films slaughtered - including the main man himself - you just think, what's the point? Sooner or later everyone is going to die, even if they do escape a trap, they'll just be brought back and continue to not think outside of their own boxes so they'll just get hacked up again. With the first three, particularly the first and to a lesser extent the third, you actually cared and wanted people to escape their fates (I could have barely given a thrupny toss about those in part two, bar Donnie Wahlberg).
Another gripe is the sheer scale of the tricks, devices and so on. The scale of the devices is getting a bit silly now, particularly the main set piece in this fourth outing. It's just too big, too flashy and too designed. The great thing about the first film was it was just some grotty old bogs in a grotty old tiled room and the premise of their predicament was fairly simple, yet still terrifying and horrific.
Inevitably this was going to happen to the franchise, everytime you show a bit more and get a bit more outlandish, you have to go further the next time...but can't you just make it more mentally torturous than visually icky? 100 ick units and 0 mental units (to use a bizarre equation I've just cobbled together) is nowhere near as good as 50 ick units and 50 mental units.
The sheer thought of the predicament in the first "SAW", plus the adequate (and at the time actually fairly extreme) gore was an ideal combination. No doubt this won't be the case for "SAW V" or "VI" (which are to be shot back-to-back apparently - not a good sign, most back-to-backs usually suck, and this late in the day as well - have they not seen "Return of the Living Dead 4 & 5"?!)
But to end on a higher note, what I did enjoy about "SAW IV" was the continued way the franchise circles around the same area of events and characters, minor parts from earlier films become main parts (with varied success), and events flash back to earlier events as well as parallel events. You could say that the "SAW" franchise is the new "Friday the 13th" franchise for the 2000's, but in terms of horror in general, at least this franchise seeks to link the films together with at least some depth and complexity.
I appreciate what they're doing with the franchise immensely, but they really need to look back at the first film and regain control over themselves before it gets completely ludicrous and out-of-hand. The best way to make a good sequel is to properly understand the films that preceded it, rather than the cliche of "bigger this, this and this".