St. Anger is badly produced, no question. But Death Magnetic is a complete disaster. Here's the difference: St. Anger was badly recorded (plus, the music sucked). With Death Magnetic, however, the recording itself seems fine, I think things went wrong once they started mixing and EQ'ing -- again, once you listen to the remix, it sounds much better than St. Anger. So, the "stems" are okay, only the final product is a mess. Something tells me even the stems on St. Anger would sound bad. At least Death Magnetic is fixable -- but that also makes the final product even more inexcusable. I originally thought Death Magnetic was the victim of bad CD mastering, but someone else on this thread (may have been Yax, I don't recall) pointed out that the problem was with the final mix and that even the CD mastering engineer was appalled by the sound on the tapes that he received. So, I don't know if this is Rick Rubin's fault or Lars' fault or someone else's fault, or some combination of the three. Lars certainly bears some culpability, as he's defended the sound in the press since the release. Hopefully it's not a Rick Rubin problem, for the sake of the upcoming Black Sabbath album, which he's producing. But, I stand by my statement that the retail CD version of Death Magnetic is the worst-sounding music release I've ever heard. (I'm told the Iggy Pop-remastered Raw Power album is even worse, but I've never listened to it and don't intend to start now.)
Re the debate about the production on the Black Album, Night Prowler needs his hearing checked. The production on the Black Album is quite good. That said, I wouldn't say it is better than Martin Birch's work for Iron Maiden or Mutt Lange's work for AC/DC or Def Leppard. For example, Barry Diament, a well-respected mastering engineer who worked at Atlantic in the 80s when CDs were first made commercially available, has praised the sound on Lange's master tapes from Back in Black as among the best he's ever heard.* So, I think Flash goes too far in saying the Black Album has the "best" production, but I agree with him (and disagree with Night Prowler) about the production generally.
Re Lars' drums, according to one of the Metallica documentaries, they hired Bob Rock because they liked the drum sound on Motley Crue's Dr. Feelgood (another well-produced album) and they hoped he could replicate it -- which he did. The difference in the drum sound from And Justice to the Black Album is striking. The drums are definitely goosed up in the latter, which was the intention. If you don't like it, fine, but Bob Rock competently did what he was hired to do. (Of course, that doesn't change the fact that Lars is a mediocre drummer.) I prefer the drum sound on the Black Album to that of And Justice, but neither sounds as good as the drums on Master or Lightning, in my subjective opinion. But objectively the Black Album has a much cleaner, more polished overall production than any of those other albums.
* EDIT: This takes me back to my original point about CD mastering being so important -- even with a great-sounding master tape, a CD mastering engineer can still fuck things up. The original '80s Atlantic CD release of BiB, mastered by Mr. Diament, sounds awesome. The Atco remaster done by Ted Jensen in the mid-90s doesn't sound nearly as good, and the most recent remastering, by George Marino for Sony, sounds affirmatively awful. But it still doesn't come close to the aural train wreck that is Death Magnetic.