A person writes a famous trilogy, launches a celebrated literary and non-fiction career, and then thirty years later, when he is in his sixties, adds a fourth volume, reopening the spigot to yet another sequel and then a pair of prequels. Has this ever happened before? The closest example I can think of Lord of the Rings with Similarillon tho' I don't know of any multi decade hiatus. Maybe Dune spread out over years?
Anyway the long and the shot of it was that of course this could have been very weak. But, surprise, it wasn't. Asimov apparently kept up his writing skills in the intervening decades, and his return to scifi and in particular his magnum opus is a fitting and proportionate addition to the pantheon. The result is a 150000 word epic covering two plot threads: bureaucratic infighting by top minds and a quest by researchers for mankind's forgotten home planet.
The result is not quite space opera and not quite buck Rogers. There is definitely the element of the camp in this and the other foundation works, but Asimov also provides plausible development of some of the key forces animating his earlier trilogy, and one almost assumes "he was writing this in his subconscious for thirty years". We also pick up a little of Asimov's experiences as a tenured professor; deep structure might very well include 'campus novel' among other threads.
Foundation's Edge is for hard-core Found. Fans, fans of "hard" sci-fi, fans of the Golden Age. Since it is also the series both Asimov and posterity called Asimov's best, it is also the best entry for generalist readers. 4/5 some camp sequences, and work develops rather than revolutionizes earlier trilogy