The anatomical references to the Death Magnetic cover started as soon as the artwork was released even before the album came out. Lars and James have both joked about it, too.
Regarding St. Anger, I actually like it. I'm an old guy who despised nu-metal and think of nu-metal as typically involving some rap or hip-hop elements (so St. Anger doesn't qualify) and no solos (which does apply here), but St. Anger never struck me as nu-metal. It's not typical Metallica, of course, but I like it sort of in spite of it not being traditional Metallica as a snapshot in time of where they were at that point in their careers. And as James has said, they had to make that album to move on to what they did (better) next.