The only books he wrote in the 80s i did not like are "prelude to Foundation" and "Forward the Foundation", and "Foundation and Earth" was pretty disappointing too.
And having re-read the originals (and not the translation) recently, with my new outlook and all the books i've read since, i'd say that even those are written better than the two first Foundation books (that i love). I'd say the "Cave of steel" was the best written of his books from the 50s, a bit better than "Naked Sun" and "Second Foundation", or at least better paced. But his best books are either "Foundation's edge" or "Robots and Empire", at least to me.
