We begin with Jigsaw's autopsy, presented in gruesome, painstaking detail. It's so vivid you can't help but laugh at all the time and expense involved in producing the scene, especially considering it's entirely unnecessary. Whoever created the fake head and torso for them to tear apart, though, that person deserves a raise.
Even from beyond the grave, Jigsaw is up to his old tricks. The game this time involves Rigg (Lyriq Bent), a fairly bad cop whose primary attributes are recklessness and hotheadedness. He's intent on figuring out who Jigsaw's accomplices are, which makes him a perfect candidate to be toyed with by those accomplices.
Through the usual means of recorded messages, Rigg learns that he has 90 minutes in which to save the life of his old partner Eric Mathews (Donnie Wahlberg), who disappeared six months ago and was presumed dead but has in fact been kept alive all this time, pretty much just so he can be used as bait for Rigg. When you see the conditions under which Donnie Wahlberg must spend the entire film, you will be sad to think how badly he must have needed this job.
With the 90-minute deadline firmly established, the film makes the bold decision to go ahead and include several hours' worth of events. Suspects are interrogated; fiendish traps are explained and activated; critical police legwork is accomplished; and all of this supposedly happens in less than an hour and a half. By comparison, TV's "24" is a starkly realistic example of time-based fiction.
While Rigg is doing his thing, his commanding officer Hoffman (Costas Mandylor) and FBI agents Strahm (Scott Patterson) and Perez (Athena Karkanis) are investigating him, since evidence at the first crime scene seems to implicate him. They're also talking to Jigsaw's ex-wife (Betsy Russell), mostly because, hey, why not? It's not like there's a 90-minute deadline or anything.
Darren Lynn Bousman is back as director, having made all the films except the first, and his preference is still to shoot everything as if he were a film student making a Nine Inch Nails video. You get that metallic swooshing sound effect over everything, jittery jump cuts in the middle of people's sentences, and eerie, atonal music playing almost constantly. All of these devices are employed even in the non-suspenseful scenes in the hopes of creating a false sense of intensity.
This installment has going for it what all of the others have had: a few devilishly clever torture scenarios, and an ironic twist at the end. It's what "The Twilight Zone" would have been if Rod Serling were less subtle and more evil.
What this installment has even more than its predecessors is howlingly bad dialogue, always delivered with faux-dramatic movie-of-the-week vehemency. Jigsaw is more a nuisance than a terror now that he's dead, but at least he doesn't yell all the time. These cops act like they're auditioning for the road company of "Law & Order: SVU."
It is impossible to take a movie seriously when the movie obviously doesn't care if you do or not. Everything that's not set in a Jigsaw torture lair is tedious and over-acted. They've obviously given up on everything except the gore sequences. But even with those, the more sequels we see, the less we're going to be impressed (or scared, or titillated, or horrified) by Jigsaw's creative ways of killing people. Even if "Saw IV" were as mildly thrilling as "Saw III" was, it would still be a disappointment, simply because we've seen it before.