We went to see Riddick over the weekend. Avalyn and i thought it was pretty good. Her sister wasn't so hot on it. It's very much what you'd expect from a sequel to Pitch Black, notably unlike the actual sequel. (Love it or hate it (personally i liked it) you can't argue that Chronicles of Riddick wasn't a very different kind of movie.)
The beginning is pretty notable. Almost right at the start they go through a flashback explaining how Riddick did a crappy job of being leader of the Necromongers and due to a coup ends up getting stuck on an abandoned planet. (This was in all the trailers and synopsis, and the entire premise of how they were able to get back to the Pitch Black formula, so i don't think it really counts as a spoiler.) However aside from that flashback the first... 15? 20? minutes of the movie is all about Riddick on his own figuring out how to survive on this planet and _almost_ entirely without him saying anything out loud.
After that, well i can't imagine it's really a spoiler to say that other people show up at some point at least some of them want to kill Riddick. This is the point at which we start getting dialogue again, and there's a lot of good banter going on.
So after that it's action, banter, action, banter, etc. Lots of people and things get killed. I'm pretty sure only one such death is notably gruesome, and even that one comes off as slightly cartoony. Lots of alien animals/monsters get hacked up of course, but i don't usually find that very problematic, at least not in a visceral sense... so to speak.
Although i guess i should say that the first-aid Riddick has to do on himself in the first part of the film is a bit gruesome if that kind of thing bothers you. I'm not fond of such things myself, but i was able to get through it with only somewhat averting my gaze.