Must admit it is mainly the grooves and clever use of some amazing rsamples that is what I like most, however, sometimes the rap itself can transform a song - Empire State of Mind being a good example; when I hear the Alicia Keys solo version I'm always anticipating the different texture as it were of the rap.
Cultural appropriation - whole new thread (and I think it would get locked very quickly), but I do think the term should be cultural misappropriation.