Glowy-eyed murder-alien/professional growler Riddick (Vin Diesel, who gets to do whatever he wants in between Fast and Furious films and chooses to do this) is on the run. Far from his home planet of Furya, he's dumped onto Not Furya (yes, really), a scorched, Golden Grahams-hued digital death experience populated by Hyena Zebra Doggies that eat Riddicks and Scorpion Cobra Monsters that eat Riddicks and Hyena Zebra Doggies. Understandably, Riddick and the cool cape he wears would like to leave this place, but first he's going to tame one of the Hyena Zebra Doggy puppies, teach it to fetch, balance space-pistachios on its snout and communicate with the animal telepathically. And he's going to do that after vaccinating himself with the venom of a Scorpion Cobra Monster, squaring off against one of the biggest specimens and slicing off its stupid face, a major accomplishment because those things don't even really have faces. This extra long opening sequence features Riddick narration designed to tell you not much except that "the whole damn planet wanted a piece of [him]." But you knew that already because of the fighting.
The rest of the film involves you not needing to have seen any of the pre-this-one Riddick products. All that matters is here and now as Riddick activates a homing device in order to attract a gang of bounty hunters. His plan: kill them, steal ship, go, movie over. The bounty hunters help him out by showing up and making pronouncements such as, "I've come all this way to collect your head in a box," which is a saucy enough line to warrant both laughter for its grandiose stupidity and respect for its swagger. The rest of the human yapping is almost exactly like this, a choral fugue of bone-dumb bluster and erratically spiking testosterone levels.
One of the people who wants to murder Riddick is talented Spanish actor Jordi Molla (he of the head in box threat). There's also Bokeem Woodbine, wrestler Dave Bautista as The Very Large Guy, The Canyon's post-teen Nolan Gerard Funk as a religious sniveler and Battlestar Galactica's Katee Sackhoff as a hardened, ass-kicking lesbian who gets to be the object of a variety of rape threats because, you know, vagina. Producer Diesel thinks this kind of thing is charming, apparently, a way to woo a man-hating character to finally coming around, Gigli-style, to seeing the glory of getting it on with a guy made of extra dense Nerf footballs. It ain't.
Anyway, none of these folks murder Riddick because then there'd be no Riddick and Diesel would have to figure out some other way to avoid The Pacifier 2 while waiting for Fast 8. Instead, the antihero acrobatically dispenses with pretty much everybody he isn't planning on sexually assaulting and those murders are very cool. The killings arrive with the best-worst Space Jet-Ski chases in all of film history playing out against the grooviest of painted backdrops topped off with the kind of dialogue that was written to be repeated out loud over and over while high on something and giggling until hiccups come. Ignore the parts that trouble you and there are plenty of nonsensical sci-fi moments of idiotic monster bliss to lull you into a B-movie stupor. Don't ignore that stuff and you'll be left thinking hard about the star/producer's need to cinematically concretize his own weird fantasy life, one where being a brute means never having to say you're sorry, where the woman finally comes to you begging for it. Totally happens like that all the time, bro.