Recommender systems provide users with content they might be interested in. Conventionally, recommender systems are evaluated mostly by using prediction accuracy metrics only. But, the ultimate goal of a recommender system is to increase user satisfaction.
A. Bellogin, P. Castells, and I. Cantador. Proceedings of the fifth ACM conference on Recommender systems - RecSys 2011, page 333 -- 336. ACM Press, (2011)
P. Adamopoulos, and A. Tuzhilin. DiveRS 2011 – ACM RecSys 2011 Workshop on Novelty and Diversity in Recommender Systems, New York, NY, USA, ACM, (October 2011)