Riddick nicely undoes the mess that Chronicles of Riddick made of the Riddick story.
That previous sentence has too much Riddick in it, but the point it makes is that the next Sci-Fi/Horror flick with Vin Diesel wearing the scary-eyes will very likely have the right amount of Riddick in it. I think they've saved the franchise.
I loved Riddick, and had a blast in the theater. If you've seen the trailers, you're probably expecting Pitch Black Redux. I know I was, but I loved Pitch Black, so I was willing to take that chance.
MINOR SPOILERS FOLLOW:
Don't sit around waiting for Pitch Black Redux. That's the third act. The first act is a survival story, which I loved. The second act is a prey-becomes-the-predator story, with Riddick as the scary monster, which I also loved. The third act puts paid on all of this with a hearkening back to what made Pitch Black so much fun, only without depending on that for anything besides the nod, and when it was done I was very satisfied, and was ready to see whatever comes next in the Riddick franchise.
As an added bonus, Riddick nicely strips away the "Conan the King" trappings we were left with in Chronicles of Riddick. It's a reset, taking our anti-heroic protagonist back to his vicious, solo-act roots.
There are holes in the science, to be sure, but the way in which the characters interact with their techno-tools was so believable and so easy to relate to that I was willing to leap all the way in and just assume that the rest of the science was fine. Certainly somewhere, under the covers, buried in the back-story or the liner-notes, were answers to questions like "what do these apex predators usually eat?" and "how long is this food chain, anyway? Are there potatoes?"
It's R-rated for all the usual suspects -- language, violence, and brief nudity -- and I think it needed to be. Acts I and II wouldn't have worked without a bit of graphic crunch to them.
Riddick comes in at #6 for the year for me. I really enjoyed myself.