As far as I can remember you were non-committal about Childhood's End*: I suppose you were afraid that you might raise my expectations too high and lead to disappointment. If that was your aim, it has succeeded, for I came to it expecting nothing in particular and have been thoroughly bowled over. It is quite out of range of the common space-and-time writers; away up near Lindsay's Voyage to Arcturus and Well's First Men in the Moon.
[...]There has been nothing like it for years: partly for the actual writing--'She has left her toys behind but ours go hence with us', or 'The island rose to meet the dawn', but partly (still more, in fact) because here we meet a modern author who understands that there may be things that have a higher claim than the survival or happiness of humanity[...]
It is a strange comment on our age that such a book lies hid in a hideous paper-backed edition, wholly unnoticed by the cognoscenti, while any 'realistic' drivel about some neurotic in a London flat--something that needs no real invention at all, something that any educated man could write if he chose, may get seriously reviewed and mentioned in serious books - as if it really mattered. I wonder how long this tyranny will last? Twenty years ago I felt no doubt that I should live to see it all break up and great literature return: but here I am, losing teeth and hair, and still no break in the clouds.
And now, what do you think? Do you agree that it is AN ABSOLUTE CORKER?
~C.S. Lewis, Collected Letters of C.S. Lewis: Volume III, Letter to Joy Gresham, Dec 22, 1953
*Arthur C. Clarke, Childhood's End (New York: Ballantine, 1953)
Joy Gresham showed Clarke the letter from Lewis, and when Childhood's End was published by Pan Books of London in 1956, parts of his letter were quoted on the back of the book.