We can't really rate any art something as exceptional, because beyond good it all comes down to personal preference. For example for music, people can agree that some composition, whether its rock or dubstep is well produced, but individual style and preference will make someone either like it or not like it.

Beyond that, its called hedonistic adaptation, and its a real effect. If you get something good in a small amount, you are going to inflate how good it is. If you get that good thing in larger amounts, its going to seem less good.