In my mind, Riddick had a lot of potential after his introduction in Pitch Black. He's an anti-hero, and with that label, the capacity, if not the inclination, to do the right thing for mostly right reasons. Chronicles of Riddick solidifies Riddick in a way that I'm unhappy to see him go. [Spoilers]
We don't know Riddick's origins from Pitch Black - we're not even sure Riddick knows them. We know that he's been escaping capture for the majority of his adult life, but not why he was captured initially. He's certainly not moral, but we can identify with his want to be free. Solidifying his background with an insufficiently complex story would be such an injustice to that potential. Thankfully, very little of Riddick's background is revealed.
It seems the backstory does exist, and is revealed somewhat in the novels, comics, and animated video. I probably won't read the first two, but may watch the second. But they shouldn't be required resources for the movie, and given the format restraint on time, it was probably better left out.
The Necromongers, however, deserved more description on their history. What made them do what they did? Riddick is enough of a mystery for one movie, and without an understanding of their motives, the Necromongers aren't solid enough to be fearful. Their leader's half-death
is only hinted at - what does it mean, and how does it drive him?
Crematoria is at once a great setting and a waste of time that could have been used to flesh out the Necromongers and show off more of Riddick's good qualities. It serves mainly as a means to introduce Kyra and show Riddick's selflessness (or overriding self-confidence?) to save her.
Riddick's solidification of his time after Pitch Black makes him a saviour of the universe from a mere survivalist, and places him in a position of power that will be hard for him to escape responsibility for. Having that in your background is going to change someone - no matter how emotionally dull Riddick is claimed to be.
Kyra, given her short screen-time, threatens to steal the entire show for me. She's evolved from scared Jack into a razor-wielding survivalist in Riddick's footsteps - including that she coming into her own in prison. She's mostly confident and worldly, but that doesn't prevent her from misjudging situations and her abilities, and her to need help (whereas Riddick just needs someone to play decoy or backstab). Just a few minutes of her on-screen, and I get this feeling of potential (maybe it comes from my fantasy reading and roleplaying/world-building background).
The rest of the movie disappoints in its mediocrity - some stereotypes, tired effects, uninspired fights. I will admit to having some emotion when Kyra gets it - before I figured this would be the tie-in with a sequel where Riddick uses the powers of the Necromongers to go to Underverse and save her. Or something.
Chronicles of Riddick will probably disappoint if you liked the concept of Riddick from Pitch Black. If you liked the Pitch Black setting, you'll like the detour to Crematoria and little else. But it may be worth watching to see Kyra become a character concept. And it might be useful to watch before the sequel arrives. Or just read the book?