A good recommendation has three aspects:The emphasis on credibility is insightful. Recommendations that are too obscure may be perceived as low quality because the user cannot easily and quickly evaluate them.
familiarity - to help us gain trust in the recommender
novelty - without new music, the recommendation is pointless
relevance - the recommended music has to match my taste
This is just one of many examples of the yawning gap between predictive accuracy -- accurately predicting what people want to buy next -- and perceived quality -- the usefulness of the recommendations to users.