I've stayed at Music, Sports, and Pop Century.
I think Music rates lower simply because the icons and decor are not as exciting as the other value resorts. People find it boring compared to Movies or Sports.
Music is my favorite value resort because it's the quietest. I've been there several times, always in teh Braodway section, which is the farthest from Melody Hall, and found it peaceful and relaxing. I have never had run-ins with rowdy tour groups or loud kids, and I'm always able to get a room close to the parking lot for easy access to my rental car, which puts me farther from the noise of the pool areas.
I'm also a fan of the food court at Music. The food court at Sports was just as good, though the food court at Pop left something to be desired in quality.
I've always found the rooms at Music to be spotless and the Mousekeeping to be excellent.