My brother had this same complaint about the device not showing the heart ratings. I'm not that big into rating my music yet but may do so sometime in the future.
However, I think that the heart or broken heart is a great system. I tend to either like something or not. If I rate something as just okay then I'm obviously not that into it. Therefore, I'm probably not going to enjoy listening to it very often so why bother?
Even though I don't rate very often there should still be a visible rating system if you have the option to sort by rating. Only seems logical...