For the record, I like a lot of things about the Saw series, even things that I'm sure many others don’t care for.  I like the intentionally ugly lighting and the uniform color schemes, which feature grays that are greenish and smeared silvers tinged with dirty blues.  I like the apparently recycled sets from the previous movies and especially like that all of the sets—police station houses, seedy apartment buildings, etc—seem to be variations on Jigsaw's lairs, with their endlessly underlit hallways and portentously grimy doorways.  Most importantly, I don't mind the Hollywood musical- or martial arts-movie-approach to its own set pieces of torture and bloodletting:  as long as a narrative or thematic rationale hangs loosely in the background, I'm okay with them in principle.  (Although when the set-ups seem blatantly for the audience's benefit—the nude woman blasted with water in Saw III—it pops me out of the reality of these movies big-time.)

What else don't I have a problem with?  Well, there's the pumping up of minor characters into major ones in order to fuel the storylines; in fact, at times that device actually comes across as resourceful.  I'm also fine with the fact that most of these characters are deeply flawed or just downright nasty—to me, the importance of audience "identification" has always been overrated.

That said, I wanted to shout at Saw IV like one of its own pleading victims, begging it to cough up some characters who are interesting in one aspect or another.  The first Saw did that.  The second a bit less so, with its introduction of the stock "troubled cop" character played by Donnie Wahlberg.  But at least it made the attempt, an effort bolstered in that movie and its successor by the presence of Jigsaw's protégé, Amanda.  Saw III had a couple of interesting characters—I don't mean that they were fascinating, but they were substantial, sometimes unpredictable folks whom it was "worth" putting through the ringer to see how they'd respond.

Saw IV, however, doesn't even really try hard in this department.  Using a shotgun approach, the movie introduces or re-introduces several major characters but all of them are less compelling than the little marionette-like dude that Jigsaw uses as his mascot/mouthpiece. There's Rigg, a SWAT leader whose crime is that he cares too much and can't "let go."  Sounds more like a premise for an episode of Dr. Phil than a springboard for a grueling horror film.  There's Costas Mandylor, playing a better-dressed version of the stock-cop.  There are a couple of FBI agents who reek of cardboard and there's also Jigsaw's ex, played by Betsy Russell, a character who ends up being less important than her build-up would imply.  At different points in the movie, all of these individuals serve as our point-of-view characters, and there's nothing wrong with that, it's just a bit ambitious.  The problem is, you've got to make at least a couple of these characters capable of being strong change-agents in terms of the narrative.  In other words, if we keep in mind the old adage that a thriller is only as strong as its villain, and a horror movie as strong as its monster, the filmmakers seemed to have forgotten about the other side of the equation:  the audience needs a solid protagonist to pit against the antagonist and thereby drive the dramatic tension.  In Saw IV we don't have anyone remotely like that, just a gang of caricatures who look like they wandered onto the set from various cancelled TV series, they're that bland and generic.

But here's where I'm not keeping my word:  I stated at the outset that the movie messes up the details, but I'm dwelling on elements such as character and dramatic structure.  Big problems.  So maybe if Saw IV had hooked me with a compelling through-line, instead of twists that are really just retreads of the surprises in the first two movies, than the smaller problems wouldn't have stood out as much.

"What problems?" you ask

In the opening autopsy scene, Jigsaw's face/head looks so fake that it detracts from the otherwise effective gore effects.  And this is not entirely a slight against the team responsible for those effects—the director, Darren Lynn Bousman, could have easily shot the scene more obliquely, but he is too busy, like a stage magician, pointing out that there are no tricks up his sleeve:  "Jigsaw really did croak, see?"  He tries too hard to deliver the shock effect of showing our monster not only dead, but also nude and butchered, yet the scene achieves the opposite result, coming across as so calculated and false that the gory imagery is surprisingly ho-hum.

In the same vein, actor Tobin Bell often appears significantly older in the scenes set further back in time.  Again, some of this may be unavoidable as the real man does age, but a lot of it results from how Bousman decides to shoot Bell, over relying on close-ups, as well as how the DP lights him, doing nothing to soften the lines in his face.

There is more than enough blame to go around, though.  Screenwriters Patrick Melton and Marcus Dunstan are to be acknowledged for doing a good job with the pacing and the intersecting subplots, and for creating some inventively gruesome "tests" for the victims.  However, the story itself ultimately never seems to go in any unexpected directions.  Moreover, some of the overheated dialogue just plain stinks.  For example, Agent Strahm's interrogation scenes recalled nothing as much as the analogous scenes in There's Something About Mary (1998).  It's a bad sign when the director has to resort to making a character's fist explode against a wall with the thunderous sound effects and multiple-iterations of a roundhouse kick in a kung fu movie in an attempt to dial up the drama.

And the thing that really disappointed me in some final, definitive sense, is that Bousman and editor Kevin Gruetert apparently got lost in their own labyrinthine storytelling.  With so many flashbacks in a movie such as this, it's important to keep track of who's "authoring" each one.  And yet in one scene, told by Russell's character Jill, we actually see her exit the flashback's setting and the action still continues for a while by following Jigsaw/Bell.  So how exactly does she know what happened then, or are viewers not supposed to care anymore about basic cinematic logic as long as we're served up a big, juicy twist at the end?