Morrowind has one of those memorable soundtracks for me that i'll always remember, like Guildwars, Baldurs Gate, Outcast, Command & Conquer, and Diablo... backgroundy is good. backgroundy never gets boring. backgroundy doesn't impose on the game, it enhances it. I'm hoping that Oblivion is the same.
Come to think of it, although I didn't notice the Morrowind music that much, the reason I really love the first track on that one is because it has the tune from Morrowind.