Felt same way after the black album, but All Nightmare Long off Death Magnetic is one of their best, IMO.
The first four are mandatory metal records. The self-titled is very well done, but the beginning of the end (I'm not fond of it).
I bought Ride the Lightning as a new release and had a Metallica patch on my jacket in 1984. Bought Cliff 'Em All on VHS.
Fact is, Metallica has stunk for WAY longer than it was great.
Lars' skills have gradually deteriorated (and he wasn't a studied and accomplished drummer to begin with), James has forgotten who he once was (and his well of riff genius has been dry for decades), Kirk has revealed himself to be a very limited, sloppy and unmotivated guitarist, and Robert just doesn't belong.