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)