I brought up the Covenant/Land comparison for a reason. It's the eternal problem of having a super-successful series/character/world.
People always want more of it.
For example, a someone who loved the Chronicles of Amber, I was thrilled to see that Zelazny returned to them with the second Chronicles (the Merlin Chronicles). And they were ... fine. But they weren't essential. And they weren't as good as the Corwin Chronicles.
It's that eternal battle- I'm glad that I got to return to a world I loved to read about, I'm glad that Zelazny got to get more checks, but it was also so inessential compared to what had come before.
It's the same with the Covenant series- although I think that you could almost say that the first two trilogies were the original, seminal work, and the recent quadrology was the belated afterthought. Sure, it was fine, and it was good to return to the place and the characters ... but it was just so monumentally inessential and lesser than what had come before.
I'm hard pressed to think of a good example of a writer returning to something after a period of time, and having it matter. I know it exists, but usually it's ... you know, fine.