Unsurprisingly, given the 30-year gap between publication dates, Foundation's Edge is a very different beast to its supposed predecessors, Foundation, Foundation and Empire, and Second Foundation. For one thing, it's much longer, at 430 pages (as opposed to 240 for Second Foundation), and for another, it has only a single plotline, followed throughout the book, instead of several episodes designed to illustrate one political movement. And, of course, Foundation's Edge is where Asimov goes all clever and decides to incorporate ALL HIS STORIES into one arch-narrative in a vast and all-encompassing marketing ploy designed to make his readers scurry off to get the full story, as it were. There's even an Afterword which helpfully points out which books to buy.
Foundation Councilman Golan Trevize begins to suspect the continued existence of the Second Foundation, despite its apparent destruction at the end of Second Foundation. To prevent the retaliation of the Second Foundation if and when these doubts become too vocal, President Coin-type Mayor Harla Branno exiles Trevize, sending him off into the Galaxy with academic Janov Pelorat with the ostensible goal of finding Earth while covertly hunting for the Second Foundation. What they actually find, however, is startling, strange, and entirely unexpected.
So there were good and bad things about Foundation's Edge. I loved the extended glimpses we got of other worlds, with all their strangenesses and odd customs: Trantor, dead planet-city (although sadly not the Imperial Library); Sayshell, with its stories of wrecked fleets and robots; and the wonderful Gaia, a living planet in the true sense of the word, one vast consciousness working through individuals to Make the Galaxy a Better Place. And, yes, I did enjoy the encroachment of the robot stories upon Asimov's space opera, because, well, ROBOTS IN SPACE.
I'm slightly uneasy, however, about Asimov's attitude towards his female characters, who, by the way, he describes with a kind of voyeuristic detail which he never extends to his male characters. Do we ever hear about Trevize's muscular thighs? Do we heck. All of the women in Foundation's Edge are either manipulating, power-hungry politicians (Branno and Delarmi) or objectified pets (Novi and Bliss). Novi and Bliss, however, are both revealed to be more important and more powerful than they seem by the end of the book; I'm not sure if that changes anything, but it's also true that they are repeatedly underestimated by their male counterparts. Apparently twenty-two centuries, Galaxy-wide expansion and psychic powers have not been enough to abolish sexism.
Oh, and apparently Trevize's spaceship runs on "the fundamental energy store of the Universe". Our scientists can stop working on cold fusion, then.