I heard it was rather repetitive, but I saw my friend playing it and the graphics and music stunned me. SO GOOD. And so free-moving! O_O
Ultimately I'll not get it, since I prefer Prince of Persia (the first one, mostly), but that doesn't stop me from listening to the music about 9 billion times a day. Go here for an idea of why the music rocks so much:
http://youtube.com/watch?v=VCZmVzRVM9oIf you want to hear the exciting chase music in the game, go to around the 7 minute mark in the 'Access the Animus' video (which should be on the right hand side of the above video).