Without turning Graf's thread into a hellthread I have a theory about Metallica that I'd like to share. Metallica have three eras, and they have nothing to do with who was playing bass at the time.
Era one was the period from Lars and James starting the band to the end of the Black Album touring cycle. This was the time when the band made their mark, dealt with tragedy, and eventually reached the top of the heap.
Era two was the period following the long break before Load to the end of the St. Anger tour cycle. This was the "well now what do we do" period. They had carte blanche, and used it to make Load and ReLoad (Load was a decent album oriented rock album, but this is a problem when you're known as a metal band with "metal" in it's name. ReLoad sounds like leftovers, because it is leftovers.) and then followed that with a covers album and a symphonic album. Hardcore fans felt justifiably alienated, and casual fans were confused. The anti-Napster crusade didn't help matters. The end result of this era was the departure of Jason, the first rehab stint for James, and the difficult gestation and birth of St. Anger.
The third era started with a band not sure of who they are. They made the strategic decision to make an album that was specifically meant to win back fans (Death Magnetic) and toured extensively. They didn't give up entirely on experimentation, as they did a poorly received album with Lou Reed (Lulu) that the less said about the better. They then doubled down on the Death Magnetic sound with Hardwired...
The sense I get with this current era is that the band understand that the entity known as Metallica is bigger than the 4 individual members, and they recognize that maintaining this entity requires significant effort. Having said this they are really close to falling into the trap Iron Maiden have been in for most of the last 15 years: "Well, we can't do anything to alienate the fans as they are the only ones still buying our albums, and even if we did something new no one would care because we have been at this for 45+ years."