I disagree. It does sound bad. I don't see how rapping like Chief Wiggum could possibly have made the song any better. Yes, some people talked like that in the 20s and 30s. So what? He didn't need to throw on a lame voice to get into character, nobody would have called him up on it had he used his normal rapping voice. Nobody would have said "His voice is historically inaccurate, people spoke differently back then". It was a bad decision on Nas' part.