This almost isn't a horror movie at all--it's a crime thriller in the tradition of Seven or Silence of the Lambs, but this time, we spend a lot more time with the victims than with the cops. I guess Along Came a Spider kind of does that too, right? Without the games/rules subtext?
So I was pleasantly surprised by the narrative continuity here--it's not all senseless gore. Sure, I think Octo is right in his review that the rules of the various games don't really add up to a coherent worldview for Jigsaw, but the overall idea of a serial killer who creates game scenarios and then watches the victims play for their lives is fairly consistent. Jigsaw's bluster about wanting to teach lessons can't be taken too seriously, though, as Octo points out.
Pudgy Cary Elwes has come a long way from Princess Bride, here, btw, though Danny Glover is still playing the same tired old cop he always plays. Seriously, I was hoping the script would have him say, "I'm gettin' too old for this shit" at some point.
The twist ending I thought was somewhat clever, though I'd sorta recognized that actor when we see him in the early cancer scene. At the time, I remember thinking the killer would obviously be either the Lost dude or that other character actor on the gurney. Still, I bought into the Lost guy (notice that the sidekick cop was also on Lost?) as the killer, so it was cool when Adam found the tape at the end.
Stuff that sort of annoyed me? The montage style that Octo already obliterated is a good start, especially the hyperkinetic one when the chubby guy tries to plow through the razor wire. Also, what kind of detectives don't call for backup, EVER!? There's plenty of times when they had Jigsaw in their sights only to go running off some dark alley by themselves. Seems like that could have been fixed in the script.