I think the music would benifit from some layer changes. The idea is from Halo, what they did is play two tracks of music, the base music and the extra layer so that when a battle started the drums would fade in seamlessly. They could add this to the system and break every area into smaller zones and then give each zone it's own unique layer. Because the music is great for the zones but it is to repetive. This way they could keep the great music but the extra layers would give each zone it's own feel.