Don't discount the appeal of a B movie that's in it for the down-and-dirty fun, minus the philosophical windbagging. Such a movie is Riddick, an alternately kick-ass and clumsy piece of sci-fi claptrap that puts its empty head down and gets the job done. Vin Diesel, a graduate of the block-of-concrete school of dramatic arts, is back as the titular anti-hero, an ex-con being tracked across galaxies by bounty hunters. I say that Diesel is back because he's played Riddick before in 2000's Pitch Black (not bad) and in 2004's The Chronicles of Riddick (very bad). Why has it taken nearly a decade to get Diesel into Riddick gear again? Well, it takes time building a career out of playing street racer Dominic Toretto in dozens of Fast and Furious films (I'm exaggerating the number but not by much). To be fair, Diesel has tried acting twice—in 2000's Boiler Room (not bad) and 2006's Find Me Guilty (also not bad). But the money is clearly with Diesel in badass mode and speaking in a voice that sounds like he gargles with gravel. That's Riddick, baby. The movie looks made on the cheap, but David Twohy, who directed them all, gives the first half hour an elemental drive. Riddick, abandoned on a rainy, lifeless planet, is put upon by mud demons and various other creepy crawlies until the arrival of two bounty hunters, Santana (Jordi Molla) and Johns (Matt Nable). That's when things turn from propulsive to achingly predictable. Too bad. Riddick had me going there for a while, effectively killing time until it killed my patience.