These are just words...be not afraid...
I first heard rap in early 1981. since then it has been my experience that rap is worthless garbage and unworthy to be called "art". I've yet to hear anything artful about it. the very best rappers write at a mediocre level. and that's being generous. without violence, sex and profanity, they would vanish. it may require skill to talk really fast, just as it requires skill to eat eighty hot dogs in sixty seconds, but that's not art. Rappers are little more than pornographic auctioneers. Those that praise rappers rarely quote their work. They can't...it's awful. I just read the review of Kendrick Lamar's new cd on AllMusic.com. AllMusic is generally trustworthy. go to the site and read the glowing review for yourself. I think they quoted one line. It's trash.
In the early nineties, Ry Cooder was interviewed by Musician magazine for an article about Robert Johnson. Ry pointed out that these days people are put on a pedestal for doing nothing. (Compared to Johnson) Nothing fits that description better than rappers.
And yet using your own source AllMusic, which you say "generally trustworthy" gives N.W.A's nasty Gangsta Rap Album Straight Outta Compton, which is among the most vile of all successful Gangsta Rap ever gets... wait for it... 5 out of 5 stars and users seem to agree with their assessment. But hey, don't let facts get in your way when you're hating. So big deal, you're a bitter guy who hates music never meant to please you (nor should any music try to please people... love it or hate it, who cares what any one person thinks, everyone dislikes something that others consider brilliant). I don't even care for their stuff, but it's so easy to disprove your opinion with your own source, I couldn't resist. There's plenty of other 5 star rap albums, but who has the time. http://www.allmusic.com/album/straight-outta-compton-mw0000653426
Oh and Ry Cooders album from the same era, (he had some poorly rated soundtracks in 1988) 1987's Get Rhythm rated 3 Stars on All Music (though his legion of fans liked it better). Different Strokes.