The Black Album blows goats compared to any of their stuff that had Cliff Burton's fingerprints on it... even though the first 3 albums are very rooted in Metal, they have a Punk ethos (particularly hXc) to them that make them great.
That might sound like me being an old fart bitching that they sold out blah blah blah, but the truth is there's been plenty of artists that have "sold out" and made and make great music after becoming commercially successful.
For what it is, I guess the Black Album is not too bad. Much more bearable than their more recent stuff.