I enjoy watching Chronicles of Riddick. Obviously it's quite different to Pitch Black but I like both films. I tend to view it all like Vin says, comparable to LOTR in structure.. That Pitch Black is the prequel, the introduction to the character and universe. Chronicles is the start of the trilogy and main story that takes place in the universe. Ok, so they are 2 different feeling films but I think that's solely attributed to the rating issue rather than where they took the story.. I can totally see the Riddick of Pitch Black running about in Chronicles.
Undoubtedly, Riddick was perhaps let down a bit by the PG13 rating but I still enjoy it. I think the biggest problem it has is not so much that it's more effects/visual heavy than PB but it's more to do with the villains.. In light of what you expect from Chronicles based on PB, I don't think they quite stand up to that and again, that's perhaps to do with the rating..
Ideally, I'd like to see them continue the Riddick trilogy they planned with the same visual style but with a tone closer to PB.. perhaps a happy middle ground. It might require a step up in the rating though..
Whatever they do with it.. more Riddick is good news.