Maybe I'm just expecting more as the trilogy wraps, but it seems like it's the same old thing, same old themes. How much power does a single individual have to affect the course of humanity for good or ill? That's the question. Predestination is again explored, but there were really no new twists or insights, no shift in the status quo of the story - the Seldon Plan continues, unfailingly toward the creation of the second Galactic Empire spearheaded by the Foundation after a series of crises move it closer and closer to consolidating it's power.
The new element in this story, kind of introduced in part two, is the mysterious Second Foundation. We see for the first time the true involvement and dual nature of the Seldon "back-up" Plan. A group of psychologists and psychics affecting the course of history and preserving the plan through subtle manipulation - only this time members of the First Foundation are on to them and want them defeated. Although Seldon predicted both factions would work together to create the Second Empire, members of the First Foundation don't seem to like the idea of being controlled and wish to assert their independence from these mind masters. Oddly enough, they have no problem accepting that their future has been written 500 years in advance and that there's nothing they can do about it. The problem, from the perspective of the Second Foundation is that the First has become apathetic. Trusting in the Plan, they feel like they need do nothing to respond to crises in order to win and that could be dangerous.
I dunno. This is supposed to be genre-defining. But as it goes on it seems to just rehash with new characters. On the plus side, I really like the characters in this particular installation - perhaps the best Asimov has come up with yet, very round, life-like and very likable - especially Arcadia. I'm less and less motivated to finish this and book 4 looks more of the same from the first 20 pages, but I've been reassured that the focus changes as book 4 was written 20 years after the publication of this original trilogy.