I have not gone back to reread this in a long time; as you say, it's probably best to consider it as a period piece. Nevertheless, I think I can say that when ~ 13 year-old me encountered this (in The Science Fiction Hall of Fame, Vol. 1, which I think was 1971) it was the first short story I read that broke my heart.
About the only thing the novel has over the short story is that Charlie's intelligence increase takes longer and is a bit more believable. He doesn't have _time_ in the short story to have read all those books, even if he is a 200 IQ speed reader ...
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I never had the nerve to read the expansion; there is no way the short story could be improved.
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