At different times I've owned practically all of Metallica's albums, but I've grown tired of most of them pretty quick and gotten rid of them. Except I still love the black album, which I consider the bull's eye in the middle of Metallica's career.
The stuff before the black album isn't melodic enough, and the stuff after isn't either, but in a different way. Their worst album is their last one, St. Anger, which I consider downright unlistenable. But that black album, that's the stuff, probably in my top-ten albums ever.
I'm pleased to report that Metallica is back in the groove with their new album, Death Magnetic (cover pictured). It's a return to form on instrumentation, with plenty of phenomenal guitar. It's almost as melodic as the black album but with longer songs that aren't as radio friendly.
I don't think it's quite as good as the black album, but it's nice and crunchy and delicious, and it's a keeper. I'd like to see Metallica in concert someday.