Saw IV (2007)
Watching these films back to back a few days apart is definitely the way to see them as so far they have all been one single story line. A story line i'm sure i didn't pick up on (Other than jigsaw himself and his issues) with characters returning from previous films that would slip by unnoticed had i watched them as they originally were released with the numerous flashbacks to previous entries not really registering as they should.
As it is
Saw IV is a grim and bloody continuation of the story but seen as a singular entity doesn't have much merit aside from the gory trap set pieces (Of which there are several).
The Chicago Tribune suggested that
'The borderline pornographic violence will' turn your stomach and
'It's disconcerting to imagine anyone enjoying the vile filth splashing the screen'.
Come on, tell me that doesn't make it must see viewing?