Der Ring des Nibelungen
Wagner’s music matches each character and situation beautifully.  It develops continuously: there are no breaks in the music during the acts.  Wagner used what he called leitmotifs (leading motives).  These are tunes or chords or little musical phrases which are linked to particular people in the opera.  In this way he can hint at things very cleverly in the music.  For example: there is a leitmotiv for the curse.  Whenever we hear this curse motive we know that the curse of the ring is working.