I always thought that Load and ReLoad, just like the two Use Your Illusions albums could each have been scaled back to a single album. I realize that it is not the best comparison, because the Illusion albums were released simultaneously and L & RL were released a year apart. I'm always skeptical, though, when albums are released that close apart because it screams "B-sides and leftovers not good enough to make the album" to me, regardless of what bands claim about using mobile studios or recording between legs of tours. It is much the same as bands' second albums often have a "sophomore slump," mainly because they partly (or mostly) consist of old songs that someone didn't deem were good enough to be put on the first album.
As far as Metallica's upcoming album, I wonder if they'll use a session "ghost" drummer for Lars, much like KISS did Anton Fig when Peter Criss could no longer play in the late seventies.