Understandably regarded as a classic, not necessarily because its alternate history scenario is so plausible or richly imagined - I found his "Catholic Church prevails and stops progress" scenario not all that compelling - but because the individual portraits in these short stories are so compelling. This is far better written than most genre fiction, although the writing was a bit opaque at times. Also, as some reviewers have noted, the "Coda" is problematic, in that it reframes the entire book as a parable about science, progress, and nuclear warfare.