I really loved this episode, I was worried at the end of the last season that they would never top it out, but seeing episodes like this one it's fair to say that the series is at his best.
Nick takes the lead in a strange episode without Grissom... is not the first time, the other one I remember Warrick and Brass took the lead and it was a wonderful episode also. It's really good that they do things like this one it shows that the show is really mature and can survive without the lead (don't get me wrong, I think Grissom is the best).
I really liked the narration of Cassie along the episode, another unusual thing to see in CSI. I'm noticing in the last time how the directors bend some of the show rules and add something new to the ecuation, besides the work that Quentin Tarantino did, I liked this the best.
What I liked best in this episode is the character development for Nick, something that after "grave danger" I expect to see a lot this season. I really liked the part of the "feminin energy" and how Nick's voice breaks a little when he says he's trying to make it through this life.
I don't know the actress but I think that the little girl who plays Cassie does a wonderful job, it really breaks your heart at the end and when you hear her voice over the development of the story.
The best episode of CSI this season so far(ok, I didn't watch that far... only five episodes, but it doesn't matter).