Most rap music leaves me cold. One reason is that, as a 42-year-old white Canadian male, I am culturally predisposed to dislike it. Another is that a lot of rap is crap: monotonous, rhythmically and melodically sterile, and full of violent, misogynistic, homophobic posturing.
Of course that's the kind of thing white people said about "race music" before blues pioneers such as Robert Johnson were safely dead and thus eligible for musical canonization. But when it's done well, by truly creative artists, rap has an undeniable power and a unique vibe -- it's the language and rhythm of the streets, distilled and blended until it becomes Art.
My first reaction to Japanese rap was negative. At least American rap, even if a lot of it was mindless rubbish, was the real thing. Most Japanese homeboys are just boys who have to be home on time for okasan to serve them dinner.