Controversial Japanese director Takashi Miike unveiled "Shield of Straw" (Wara No Tate) about a nationwide bounty hunt for a child rapist who murders the seven-year-old granddaughter of a billionaire politician.
The man offers a one-billion-yen (USD 9.7-million) reward for the criminal's capture and killing.
The offer touches off a frenzy in the country, sending hordes of would-be vigilantes on the chase for the murderer.
Fearing for his life, the paedophile turns himself in and a team of cops -- a widower whose wife was killed by a drunk driver and a single mother -- see it as their duty to protect him at all costs despite his vile crimes.
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The picture, one of 20 vying for the Palme d'Or award, got off to a promising start with impromptu applause for a spectacular ambush scene executed with military precision.
But reviewers said the film went off the rails during a bullet-train scene in which the cops deliver long speeches about their personal motivations and reflections on the moral quandary they face over risking their lives to guard a remorseless killer, only pausing to brutally dispatch blood-thirsty bounty-hunters.
Movie magazine CineVue posted a review within minutes giving the picture one star out of five and calling it a "stone-cold dud" while cult film watcher Electric Sheep said it went "down like a lead balloon".
The Irish Times reviewer, however, had a few kind words for the "classy action sequences" and predicted a big-budget Hollywood remake.
"Few action movies have been so dedicated to the cause of liberal democracy and trial by jury. Shield of Straw is the anti-Dirty Harry," it wrote, referring to the iconic Clint Eastwood franchise.
"It's not the viewers who don't want to see these films, it's the professionals, the people who make films," he told reporters.