Its absolutley amazing. its jay-z's best album on top of the beetles best album. http://www.youtube.com/watch?v=m1dpkEEQO3E thats one of my favs. it such a great album.
The DJ who mixed it (Dangermouse) is also 1/2 of Gnarls Barkley btw. And in my opinion Reasonable Doubt shits on The Black Album
The Grey Album is solid, but The Black Album is definitely not Jay-Z's best album. Check out the rest of his discography. Danger Mouse is the man. It's a shame that producers are so limited in what they're allowed to sample, although I understand why the original artists might feel like they deserve a cut of the profits.