Hardcore longtime Metallica fans don't view the Black Album as a classic, they view it as the one that broke them to the mainstream. I agree with Tom that the first four albums are a whole different level.
That's because longtime Metallica fans hate anything that isn't thrashing the E string at 500bpm for 8 minutes straight.
Agreed, it's not in the same level as the first 4 albums but is a classic anyway.
I am one of those people that viewed the Black Album as a big let down. But NOT because it was different. After three VERY similar albums, it was obvious that a change of some sort was needed.
What bothered me (an many Metallica fans at the time) was that they had come as far as they had by breaking new ground and doing what they wanted to do. No radio airplay, no music videos (until One)...they were playing metal like it had never been played to the public before. What they were doing was unprecedented.
The first four albums (yes, even KEA *at the time*) was breaking new ground. But The Black Album turned Metallica from trend setters, to trend followers. TBA, while being a extremely good and listenable metal album, was pretty cliched. It was nothing that hadn't been done before. Yes it was catchy. But you could almost dance to it. That really seemed to go against everything Metallica had built up to that point.
I wanted change, but I wanted something that would continue to piss off most people. Even if they would have simplified and released some form of early groove album...but made it even heavier. Can you imagine James Hetfield singing on something more akin to Sepultura's Chaos AD??? Now *THAT* would have been Grammy worthy.