I can't recommend Firefly enough! As a dedicated "Trekkie", I STOPPED watching Enterprise for Firefly. The series (well, ex-series) has (had) multiple plots going on, some unique characters (not re-hashed stuff), and a wonderful writing staff. Check out the "Out of Gas" episode for a very good example of writing technique! Absolutely wonderful piece.
But back to River (Summer Glau). She's a "cinderella story" herself. Besides her natural ability to act the part she has, she has that pouty/soulful looks and innocent yet sexy stage presence. By "cinderella story", I mean
this. Nearly NO acting experience yet in a major Universal movie. I guess Joss saw in her the same thing I see. (grin)