It is always dangerous to revisit fondly-remembered classics from one's youth. How many times have you reread a book from your childhood, only to find it actively and acutely terrible? There's a reason I have no plans to ever reread the Ringworld books - I loved the first two when I was younger, and even remember plowing through the third when it came out in paperback (I don't remember it being very good?) - but I'm fairly certain that the books are of a type of late-century hard sci-fi that already shows signs of having aged poorly. (I have read other books by Niven that I think hold up better - his Inferno books with Jerry Pournelle are especially fun - but I don't think the world will much begrudge the premature loss of the Man-Kzin Wars series.) Although, hell, maybe one of these days I'll actually sit down and read World of Ptavvs.
But the one series I was most interested and enthusiastic about revisiting was Isaac Asimov's Foundation books. I hadn't read them since high school and didn't really remember them very well outside of the barest outline. What I did remember, however, was reading the later additions of Foundation's Edge and Foundation and Earth and being, well, pretty much incensed. As much as I loved the first three, original Foundation novels (which I checked out of the local library, in an old omnibus edition that had this awesome cover), I hated the two later sequels, so much that after I put down Foundation and Earth I didn't pick up another Asimov book for over a decade. I've never read Prelude to or Forward the. It seemed to me at the time - at least to my high-school mind - that the sequels represented an explicit rejection of the original trilogy, a misguided attempt to better the original achievement through a not-so-subtle undermining of that series' thema.
I don't want to give anything away to anyone who hasn't read all the Foundation series - and if you haven't, you should - but in his later books Asimov experienced a variant of the same kind of compulsion that Robert Heinlein experienced in his own later career. Both Heinlein and Asimov were quite prolific (although, it goes without saying, Asimov was just a bit more prolific than even his most prolific peers), and towards the end of their lives they looked back on decades of science-fiction writing and decided to pull the strands of multiple disparate novels, stories, and series together into overarching master-narratives.
Heinlein accomplished this in somewhat haphazard fashion in a series of progressively weirder (and some would say interminable) novels - Time Enough for Love, The Number of the Beast, The Cat Who Walks Through Walls and the risible To Sail Beyond the Sunset. Heinlein was a political libertarian whose stories focused on the adventures of powerful and charismatic individuals with artificially prolonged lifespans. As much as I enjoyed Heinlein when I was younger, it's hard not to see the limitations of Heinlein's formulae in hindsight: Heinlein understood historical significance solely in terms of the individual and his stories lacked any understanding beyond the level of formal contempt for the category of "society" as anything other than a temporary agreement between ultra-rational independent actors. So when he pulled together a large part of his almost five decades' worth of sci-fi production into a larger narrative structure, the result was strangely hermetic. The sum of his thousands of years of "Future History" was colonized by a handful of truly spectacular pinnacles of human achievement who transcended the boundaries of time, space, and - it must be said - morality. There's a lot of weird crypto- and actual incest and (through cloning and time-travel) literal self-love - very much in the mold of Doc Smith's strange Lensmen novels but definitely the kind of stuff to give all but the most committed libertarian pause. (After all, what's a little incest between consenting adults? Shouldn't we all have the absolute right to commit suicide at a moment's notice?) Because Heinlein was such a firm believer in the sovereign authority of the individual and the right of the individual to reject any and all political alliance save for the most immediate level of clan, his books fail to cohere in terms of producing a coherent ideal of human history as anything more than a backdrop against which high-achieving individuals could have their adventures. "History," such as it is, doesn't really concern Heinlein, because for him and his characters all history is merely a form of biography.
(I should probably take a moment to point out that Heinlein, while certainly a libertarian, was hardly a conservative in terms of his attitudes toward race, religion, feminism, and sexual independence. He just hated taxes and distrusted socialism. He was also, it must be noted, an incredibly generous person - the best example of which is the fact that he provided a great deal of material support for the far less successful [and mentally unbalanced] Philip K. Dick.)
I would argue - perhaps not an indefensible assertion, but certainly arguable - that the interaction between Heinlein and Asimov is perhaps the most significant thematic relationship in sci-fi history. You can make cases for the prominence of Clarke, Bradbury, Bester, de Camp, but in terms of quality, consistency, and influence, Heinlein and Asimov represent the genre's dominant political dialectic - rugged quasi-libertarian individualism on the one hand, and on the other demure technocratic and vague (but only vague, considering the real-world political climate) leftism. Of course, this relatively simplistic dichotomy faded from significance with the rise to prominence of authors such as Dick, Vonnegut, and Delaney, a move that mirrored a similar expansion of real-world political focus from the confines of the Cold War. But in terms of the genre's most fruitful mid-century period, it's all about the contrast between these two gentlemen - one a crisp ex-naval officer, graduate of Annapolis, scholarly dilettante and amateur stonemason - and the other a tenured PhD (biochemistry) with wild sideburns and a rather unfortunate fondness for bolo ties.
(Am I shortchanging Arthur C. Clarke? He's usually placed equal to Heinlein and Asimov in terms of stature and influence, but I don't think his own stories hold up quite as well. Clarke wrote a lot about aliens, in particularly the idea of first contact and the consequences for the human race, something about which neither Heinlein or Asimov cared much. Asimov is famous for almost never writing about aliens - only a couple examples of alien stories in his entire corpus - and while Heinlein wrote more often about extraterrestrials, he did so less frequently as his career progressed and he became much more interested in detailing the lives of his human characters than making up space monsters.)
I think, in hindsight, that Asimov was a better writer than Heinlein. This isn't a knock against Heinlein so much except to say that both men were very good writers who stood out against almost all of their peers from the "Golden Age" of sci-fi, but as their careers progressed Heinlein became less and less able to guard against his own worst impulses as a writer. After the 1960s when Heinlein's career was secure and he could write fat, sprawling novels that bore the logos of respectable publishing firms, he got lazy. In many ways he became very complacent as a writer, and his characters became more and more smug and self-satisfied. Reading a later Heinlein novel is like spending a long car trip with your uncle the libertarian autodidact, still whip-smart and extremely charming, but condescending to an unbearable degree.
In contrast to Heinlein's rather expansive sense of self, Asimov was an uncommonly generous writer whose own worse impulses - such as they were - were far less damaging than Heinlein's. Asimov is an extremely talkative writer who almost never writes action sequences. The Foundation series is composed of stories that revolve not around characters but ideas, and which are constructed in such a way that the absolute unimportance of characters is highlighted as an explicit feature. Whereas Heinlein's Future History is really the story of a handful of individuals over the course of many thousands of years, Asimov's Foundation is the story of a set of hypotheses which are attacked and defended over the course of hundreds of years of far-future political and economic machinations. In any given Foundation story there many be only a handful of "events," in terms of something happening - but every actual event is followed by pages of exposition and investigation, in which events are exhumed and analyzed, and his extremely intelligent characters are given the opportunity to reason their ways through often opaque circumstances. They owe a lot, structurally, to mystery stories - so much of the action in Asimov's fiction is purely reactive, composed of reconstruction and supposition, followed by the empirical testing of theories and inevitable course correction.
But despite criticisms over his often bloodless prose style and stilted characters, his fiction writing nevertheless manages to convey a deep understanding of human nature. He didn't often write about sex and - like every other classic sci-fi writer - he grappled early in his career with the portrayal of women in his stories. But in his Foundation stories he was preoccupied with history, as well as the limitations of science and rationalism. With no small irony, he was a sci-fi writer with a day job as a scientist who wrote quite a bit about the limitations of rationalism and the ability of destructive human behavior to undercut even the most noble designs. Rereading the original trilogy as well as Foundation's Edge, I found that, contrary to my gritted-teeth expectations - the later sequels are definitely of a piece with the original stories. Rather than walking away disappointed that Asimov had seemingly undercut the premise of his earlier classic, I am now firmly convinced that his later sequels are worthy sequels, stories that accept the challenges set forth thirty-odd years previous and proceed onward with an understanding of the imperfectability of human behavior and the conditionality of even the based-laid plans.
If that seems vague, it is because I now realize that this topic demands more than a single day's reflection. More to come.