John C. Wright has an interesting post with the title, Great Book of Science Fiction---Yet to be Written? He identifies four features that such a Great Book would have to exhibit:
(1) Timeless appeal;
(2) Infinite readability;
(3) Relevance to great ideas;
(4) Speculative sense of wonder.
There already are some genuine candidates for greatness along these lines, and in two cases -- Mary Shelley's Frankenstein and Walter M. Miller, Jr.'s Canticle for Leibowitz -- I think the case can be made very, very plausible. There are many other lovely works in science fiction, of course, but examples of works that speak in a fundamental way to the human condition (if you'll pardon the awful cliché) in literarily great ways are not easy to find. Part of this is simply the subculture; science fiction is dominated by a pulp past and is heavily geared simply to spinning a good yarn. The more brilliant works are usually little experiments in this or that rather than something that we can point to as something that will never get old.
But there is never just one Great Book, and we live in a time in which there seem to be many quite excellent science fiction authors. But despite the fact that this is likely to result in much good reading, I don't know that we'll see many Great Books in the genre. Wright's brilliant, but he'll never write one; he lacks the seriousness. Stephenson has the sweep but he lacks the good sense that can put that sweep in a striking and straightforward narrative. Actually, that's a problem with many of the great science fiction writers of our time; too clever for their own good. Flynn has that good sense that can meld sweep with craft, but I think putting Eifelheim next to Canticle for Leibowitz shows that there's still something of a chasm to be leapt.
But, as they say, it is the Muse that decides. We are in a time where most writing is very plodding and uninspired; perhaps in all this aridity a new spring will break forth somewhere.