"then deeply disappointing at the end. I was expecting explanations and resolutions of the deep background events and actors that were shaping the story and none were given."
If you read carefully, and make a couple of reasonable deductions, I think you can come to mostly satisfactory conclusions. There's room for a couple of different interpretations of what's in the center of the galaxy, but not all that many, really.
Could you explain your own deductions, please? What are the possible interpretations?
I have read both novels, but on that reading do not feel I could be sure of understanding what's at the galactic center at all. In fact, I recall feeling puzzled and wishing it was explained, much like the parent poster. I'd love to hear some deductions and to find out what hints in the book I missed.
If you read carefully, and make a couple of reasonable deductions, I think you can come to mostly satisfactory conclusions. There's room for a couple of different interpretations of what's in the center of the galaxy, but not all that many, really.