imho, and under no influence of anything but the wandering subconscious thought of nothing at all!
musicality of rap is as similar to looking at beauty of men and women from different ethnic group. Within each level, contain element of
1) substance
2) structure
3) frequency
all this three will combine together, inorder to form the end product that we see or hear. While the end product is of fixed constant progression, but we, as the listener or the observer of beauty within diffferent ethnic group is a roving variable.
This roving variable factor determined our ablity to appreciate or denounce rap music or beauty of different ethnic group. Theres ART within each format when the frequency of the mentioned music/group coincide with our state of mind at any given time. But then, most of the time, the frequency that we have naturally often reject things that unfamilar to us in the form of action/words, "sucks, rubbish, fugly, ugly, substanceless" etc.
In short, the failure to appreciate something we cant understand, often has no connection to the inner substance of these "fixed progression end product", but more to do with our wandering inadequate roving variables of one self character.