It happens in the case of some songs that they don't strike as extremely good the first time one listens to them but after listening to them a few more times, one suddenly starts loving them. What difference does the re-listening do?
The phenomenom you describe is called Mere-exposure effect :
The mere-exposure effect is a psychological phenomenon by which people tend to develop a preference for things merely because they are familiar with them. In social psychology, this effect is sometimes called the familiarity principle. The effect has been demonstrated with many kinds of things, including words, Chinese characters, paintings, pictures of faces, geometric figures, and sounds.
The mere-exposure effect has been explained by a two-factor theory that posits that repeated exposure of a stimulus increases perceptual fluency which is the ease with which a stimulus can be processed. Perceptual fluency, in turn, increases positive affect.
The perceptual fluency is explained in detail by the article in @mrt comment.