To here previews of the Oblivion music and clips from Morrowind, click here.
My opinion: I really liked the Morrowind music, but I think that this stuff is much better. The music in Morrowind was a little bit repetitive and contained to much brass in many places. The Oblivion stuff has a wider variety of instuments in more places, which makes for better harmony and themes. This game just keeps getting better and better!