I liked it, but I went to see it sober. The first half hour or so has a neat narrative and the plot takes its time establishing where Riddick has landed, who dumped him on the hostile planet, and what kind of wildlife he has to deal with. In the words of Riddick, he has to find his animal self to thrive. As an audience, you really have to be receptive to the patient mentality of Riddick. While everyone's losing their heads, Riddick laughs it off even when he's in chains at the risk of having his own head put in a box. If there's one thing that detracts from it all, it's how cliche the plot and conclusion are. Having said that, the film is dripping in atmosphere, reinforced by the world and creatures, both of which were expertly rendered and actually felt real rather than just some shoddy CGI crap. It seems like these days most Hollywood plots bite off far more than they can chew, so it was enjoyable to see a simple plot mated to a beautiful backdrop, providing some nice viscera to appreciate.
Oh right, the film picks up right after Riddick parts ways with the Necromongers so the first half is heavy on flashbacks to what happened after the events of Chronicles, but it's not necessary to see that film to keep up with the plot.