Characters often have much time to be developed but the story is the thing that keeps you reading. Some characters get more "page time" and you get a feel for a personality but it is really about the story and the world (well, the GALAXY) that Asimov has created. As I noted before his galaxy became a template for many writers who followed.
These two books, while maintaining some of the episodic nature of the earlier ones, are much more cohesive. Some characters wind up developing more personality than you find in the earlier installments. This is especially true because these two books are basically sequels to one another. They could, effectively, be one book since the first chapter of Foundation and Earth immediately follows the last of Foundation's Edge.
Despite the large gap in time between Second Foundation and Foundation's Edge, the style stays more or less the same. The early books often had people doing things you'd associate with the 1950s (everyone smokes) and even reading newspapers. While people were still reading papers in the 80s the Science Fiction conventions had moves past.
You will read flippant accounts of Asimov saying he did this for a big check from his publisher. Maybe he did but he still wrote some wonderful books.