I actually have a few interesting books on deck
Second Foundation follows the loooooooong story arc instituted in the first book and continued in the second. Asimov visits the story every few generations to see how its progressing, and I can see why he eventually came back to it: of the 1000 year span he gave the story, the first three books chronicle about 400 years. So I guess there's more story to the story.
As the title implies, this installment centers on the second foundation, established at the beginning of the 1000 year story arc by its architect, Hari Seldon. I'm not a fan of spoilers, so I won't say more, but what I can tell you as that this set of stories is just as good as the first two, and it does help to fill in some of the blanks left by the earlier tales. It does not, however, resolve the story, as I mentioned above. One would assume that Asimov got to that in the four subsequent books, altho one of those is a prequel to the first book. I guess its fair to assume that there is a second trilogy and the prequel; that seems neat enough.