"The Chronicles of Riddick," a $90-million sequel to 2000's taut sleeper hit "Pitch Black" that follows the title anti-hero through an expanding otherwordly mythology, has been the dream project of Vin Diesel (2002's "XXX") for several years. While credit deservedly goes to the buff, charismatic actor for making the film a reality, the watered-down end result badly hinders whatever potential or worth it could have had. For one, "The Chronicles of Riddick" has been downgraded from an R-rating to PG-13, a major mistake that seems to hold the material back at every moment. And two, the script by David Twohy (who also directs) is practically incomprehensible. It isn't impossible to follow the premise and its developments, but alarmingly few reasons are ever given for why anything that happens is occurring. With little to no narrative depth or involvement, the picture becomes a thankless visual spectacle, marvelous to look at but woefully empty where its heart should be.

Set five years after the events of "Pitch Black," escaped convict Riddick (Vin Diesel), who has the ability to see in the dark, shows up on the planet of Helion Prime in an attempt to clear his name. His mission is misplaced, however, when the people of the planet are ravaged by the Necromongers, a superhuman, soulless breed of creature that wishes to turn all into one of them. The reason of why is never explained, but the Necromongers are run by the evil Lord Marshal (Colm Feore), as well as second-in-command Vaako (Karl Urban) and his wife, Dame Vaako (Thandie Newton). Meanwhile, Riddick finds the time to travel to the prison planet of Crematoria, where the rays of the sun are deadly, to reunite with young Jack, now a tough 17-year-old young woman who goes by the name of Kyra (Alexa Davalos). His devotion to her, like so many of the plot particulars, is never satisfactorily explained. Nonetheless, Riddick and Kyra are unwillingly put in the roles of the heroes (Riddick discovers he is the last of a warrior race known as Furian, and that is why he is wanted), as they set out to stop the Necromongers from taking over the entire universe.

Directed by David Twohy (2002's "Below"), "The Chronicles of Riddick" is an ambitious failure, admirable in its attempt to create a completely new sci-fi world and characters without having to be based on a comic book or novel, but perfectly lousy in bringing that vision to life. The characters are vaguely drawn, at best, perplexing in their actions and placed at a distance from the viewer. Because they are wafer-thin and there is no background given for most of them, one is left wondering why they should be given a damn about. And the how's and why's of the story are unfortunately glazed over in exchange for a series of mind-numbing action set-pieces that are almost all devoid of energy or palpable tension. The exception is a fast-paced chase through the devastated, mountainous landscape of Crematoria by Riddick, Kyra, and a group of convicts to beat the deadly rise of the sun. Otherwise, the film is painfully by-the-numbers in its wrongheaded conception as a brainless popcorn movie when the complex plot clearly called for more development and care.

As the reluctant Riddick, who doesn't choose to be the good guy as much as he is forced into it to save his own skin, Vin Diesel fits comfortably back into the role. All rippled muscles, baritone voice, and glowing eyes, Diesel is ideal as an action star, but needs to branch out from this limiting genre if he wants to have any sort of Hollywood staying power. As for Vaako and femme fatale Dame Vaako, oft-described as a futuristic version of Lady Macbeth, Karl Urban (2002's "Ghost Ship") and Thandie Newton (2002's "The Truth About Charlie") seem confused as to how they have found themselves in this overblown world of blue screens. Along with Judi Dench (2002's "Die Another Day") as Aeron, a supernatural guiding light on Riddick's quest, the three of them are wasted. Dench's Aeron, known as an Elemental, who uses the elements to configure into a solid being, had some real potential, but remarkably little is done with her or her intriguing race. As sidekick Kyra, newcomer Alexa Davalos elicits a glimmer of promise with her butt-kicking, razor-happy character, but any chance of she and Diesel forming a honestly felt kinship is overlooked as the dull action moves full speed ahead.

"The Chronicles of Riddick" is all discouraging doom and gloom, a moldy cliche of a science-fiction film without the vital feeling of imminent danger. The villainous Necromongers physically appear as, for all intents and purposes, humans with stronger than usual strength and no emotion behind their eyes. This was the wrong way to go with these creatures, who never seem to pose much threat and, therefore, are giant bores. It doesn't help that their motives, like that of the rest of the characters, are highly sketchy. "The Chronicles of Riddick" may hold dazzling visual effects and some darkly picturesque vistas, but that is where the picture's entertainment value comes to a halt. Vapid, sluggish, over-the-top, and uneventful in any meaningful way, if "The Chronicles of Riddick" didn't have the basic skills that director David Twohy does, indeed, possess, it would be comparable to 2000's laughable disaster "Battlefield Earth." That is one comparison no filmmaker should ever strive for, or mistakenly find themselves a part of.