It's not like you can besmirch the reputation of Riddick, sociopathic space scum that he is. But David Twohy, who also directed Pitch Black and The Chronicles of Riddick, the previous chapters in Vin Diesel's sci-fi franchise, sure gives it the old juvenile-detention try.

Poor Riddick (Diesel). He's been left for dead by Vaako (Karl Urban, in an appearance so fleeting he shouldn't get a screen credit) and his Necromongers on a desert planet stocked with fierce predators.

Fully half the film is a long, long, and barren prelude devoted to proving that the guy will go to grotesque lengths to survive.

Somehow along the way, in the film's only attempt to humanize him, Riddick acquires a pet. That makes Riddick the first (and one hopes the last) film to borrow heavily from both Alien and Old Yeller.

Eventually he acquires more company: two ridiculously well-equipped crews of bounty hunters looking to put his di . . ., um, head in a box. Yeah, good luck with that.

Hard to know who to root for. The crew with the deliciously malevolent Jordi Mollà and WWE heavyweight Dave Bautista has all the charisma. The posse with Matt Nable and Longmire's Katee Sackhoff has better technique.

The movie is rather gratuitously smutty, but it's comforting at least to know that centuries from now in a galaxy far away, tough guys will still be trading the same blunt banter they do in bad Steven Seagal movies.

Purely as an action film, Riddick is passable, if grueling. The problem is tonal. In previous outings, our interplanetary protagonist was brutal, sure, but at least there were shadings of noble savagery. This time, he's a sadist.

And while the earlier installments, The Chronicles of Riddick in particular, suggested the Heinlein-ian potential of mankind's future in space, this is nothing but a bug hunt.

Contact David Hiltbrand at dhiltbrand@phillynews.com or follow on Twitter @daveondemand_TV. Read his blog at www.inquirer.com/daveondemand.

Riddick **  (out of four stars)

Directed by David Twohy. With Vin Diesel, Jordi Mollà, Matt Nable, Katee Sackhoff and Dave Bautista. Distributed by Universal Studios.
Running time: 1 hr., 59 mins.
Parent's guide: R (violence, profanity, nudity, adult themes, drugs)
Playing at: area theaters