Just when it seemed the Trilogy of Shame had been completed, director Darren Lynn Bousman has unleashed yet another horror flick embarrassment in the form of “Saw IV.”

In the series’ 2004 inaugural, “Saw” treated viewers to the grisly tale of Jigsaw, a serial killer who ensnares his victims in gruesome puzzles, forcing them to choose between self-mutilation and an equally graphic death. Despite painful acting and perhaps the most unintentionally funny climax of a modern horror movie, “Saw” was a box office success: The cheap thrill of seeing someone take a handsaw to his own wrist captivated enough audiences to rake in $150 million worldwide. Every Halloween since then, after a set of annual plot tweaks and minor revisions, another reiteration of “Saw” has cashed in on this unexpectedly popular trope.

By “Saw IV,” Jigsaw has finally died, but has left an apprentice to continue his deranged crimes against humanity and good taste. After a brief glimpse into the villain’s autopsy, Bousman treats the audience to the merciless depiction of a man screaming his stitched lips apart in a vivid and generous display of gushing crimson; whether the rest of the film works depends on the subjective appeal of this morbid opening salvo.

In virtually every regard, “Saw IV” is a second-generation copy of its predecessor in a long line of tired rehashes tracing back to the original (which is, in turn, a tired rehash of Vincenzo Natali’s far superior 1997 sci-fi horror, “Cube”). And, while under the direction of James Wan, the first “Saw” managed to partially redeem itself via some grimy, moody cinematography and a twist ending that actually worked (one of horror cinema’s rarest distinctions), replacement visionary Bousman made “Saw II” look and feel like an overblown, cliched MTV self-parody. “Saw IV” continues in this tradition, again featuring lazily loud shots and fast-paced cuts, an offensively trite, industrial soundtrack and the same foolproof “psychotic clown” antagonist that has not only been a trademark cop-out of the “Saw” franchise, but the entire horror genre itself.

It wouldn’t be a proper entry into the series without the dearth of acting talent to match the bloodshed’s cringe factor, and this fourth installment finds various members of previous casts phoning in woefully clueless performances. Newcomers Lyriq Bent and Scott Patterson (although eerily similar in name, unfortunately not a cameo appearance by Death Row wife-murderer Scott Peterson) make their debut as the stock good-guy cops (Sergeant Rigg and Agent Strahm, respectively), thereby adding themselves to the series’ register of faceless protagonists. And although slain in the previous episode, Jigsaw (Tobin Bell) continues to carry the series from beyond the grave thanks to a parade of cassette recordings and chronology-damning flashbacks.

Bousman places the crux of the film’s plotline on the fragile assertion that because the mad murderer only targets people who have done wrongs in their lives (prostitutes, for example), he is somehow the film’s incongruous beacon of moral justice. That his girlfriend’s miscarriage is supposed to justify his blood-soaked cause is a pathetic and asinine attempt to make him more human and relatable. It’s nigh impossible to excuse Jigsaw for subjecting the audience to such shameless gore, and the film’s screenwriters for inventing him.

Only longtime “Saw” veterans still clinging to its meager initial potential will be able to salvage anything from this update to the series. Sado-masochists and those who could still find merit in “Saw III” might be able to enjoy this film and justify its $9 price tag (and the sojourn to North Haven’s Showcase Cinemas), but everyone else is advised to keep a safe distance.

Then again, “Saw V” is already expected to rival stale candy corn as the least-wanted commodity of Halloween ’08 — things could be worse.