The thing w/ St. Anger i that you have a band at the crossroads.
The Black album had been immensely successful, even though they alienated some old fans. Then Load and ReLoad were even more of a big let down for those fans - though I did appreciate the fact that they were trying to evolve instead of just pretending to be a bunch of uncompromising angry teenagers.
Then all the Napster crap and Newstaed leaving... I think they'd lost it.
St.Anger was an eminently crucial album, one of the most important in their history. But one that should have remained in the vaults. They had to hit that rock bottom.
As horrible and uninspired as the album is, the documentary chronicling the recording process and all that happened at that time, namely, Some Kind of Monster is a must see, IMHO. It's a look inside a totally dysfunctional band who actually has to hire a psychologist to learn to communicate again. It's appalling but really worth checking out.
The following album, Death Magnetic, as much as the sound irks me, is one of their best effort in years. But then, I never was into Metallica for production values. Even though the Bob Rock-era stuff sounded great.
If you watch the making of Death Magnetic and compare it to Some Kind of Monster, you see a band that's been to hell and back, and one of them put it, needed each other more than they hated each other, and decided to focus on that. It looks like they're having fun again.