I'm glad you mentioned the "Black Album" ANF, that was the turning point for Metallica, when they crossed over from being a Thrash Metal band to a more mainstream flavor. I like the Black Album, and have no problem with any artist/band stretching out and doing something different, after all if you don't like the new CD you can always go back and play the stuff you enjoy.
I just find it funny some hate the album because of its mainstream nature. Nowadays that album is pretty much up there with Back In Black, Led Zeppelin IV, Dark Side Of The Moon, Thriller, Sgt. Pepper and a few other albums in this very elite "all time mega-classic" club that continue to convert new fans every year, yet a lot of people hate it because for the first time Metallica really courted MTV and radio (even though "One" was a top 40 hit before, that was more a case of radio/MTV actually coming to them then vice versa). There were a lot of bad "sellout" albums in the 80's and early 90's that time has not been kind to (Kiss "Crazy Nights" anyone?") but here we are twenty years later and people are still loving Black Album, so obviously Metallica did something right.