A little too open ended for my tastes
Alvin had grown beyond the pleasures of his world, Diaspar. I expect he saw them as indolent, apathetic, soft, and disinterested. He may even have perceived them as pathetic. In any event, he certainly didn't share his people's terror of the world beyond their city. Lys was much more to his liking and, indeed, may have persuaded him to stay permanently had he not hatched the plan of stealing the machine to retain the memories that the Lysians wanted to wipe out.
As a pure hard-core science fiction entry, the tale was great - high speed mass transit using "sidewalks", faster-than-light travel, robots accepting voice and telepathic commands with built-in programming overrides and safety features, rocket ships, skyscrapers that are literally "sky scrapers", mass with properties different than the solid, liquid, gas paradigm of the day and so on. All of these speak to Clarke's vision and imagination. Some real vision on the soft sci-fi side as well - the obvious need for a reduction in birth rate to coincide with the reduction in mortality rates as health improves and longevity increases, the differing paths that evolution can take, the effect of isolationist policies, the inability of people to accept change in the face of long-standing tradition and "religious" ideas and so on.
That's it, though. Unfortunately, I give the book overall (at least, for me) a failing grade!
While the ideas are timeless and the book could easily have been written yesterday with only minor modifications in the science, I thought the overall plot was weak and watery - an obvious prelude to the Odyssey and Rama series. In my humble opinion, Clarke is perennially unable or unwilling to provide a real or hypothesized source to his artifacts and is equally unwilling to provide a real resolution to the questions posed by the artifacts. Where does Alvin go from here? What is he likely to encounter? Why would he choose to do what he does? There are also several plot questions that remained, for me, annoyingly unresolved - namely, where the heck did Alvin come from? Was he born - if so, how? Was he hatched - if so, how and perhaps even more important, why? Lys's belief that Rorden was somehow more trustworthy than Alvin in keeping the secret of their existence seems to me naïve at best, misplaced at worst and a feeble plot contrivance to allow the story to move forward. Who was Alaine of Lyndar and why did the story that unfolded with Alvin not happen with Alaine? If the climate of earth has evolved to the point that the hydrological cycle is so totally trashed and the oceans are non-existent, how does Clarke figure that humanity would survive that? With records as extraordinary as those to which Rorden had access, it seems impossible to conceive that Shalmirane, a weapon capable of destroying a moon whose orbit had decayed to the point it was "falling", would ever be relegated in history to a legendary battle with space invaders.
I've always been unable to figure out why Clarke is perceived as such an icon in the field of science fiction! Some fellow readers tell me that some of these questions get answered in THE CITY AND THE STARS. That may be so but it didn't help me out with this one, I'm afraid.
Paul Weiss