The man addressed turned slowly around and faced the speaker. His expression was hidden by a grotesque helmet, part of a heavy, leaden armor which shielded his entire body, but the tone of voice in which he answered showed nervous exasperation.Heinlein's mammoth future history, some of which I had re-read recently; 21 stories published as a collection in 1967, though in fact all but two originally came out between 1939 and 1949, outlining the future development of humanity through the coming centuries. The 1941 stories alone provided four of Heinlein's five final ballot spots in last year's Retro Hugos for Best Novella and Best Novelette.
Heinlein misses a lot of things - notably the rise of information technology; his 23rd century spaceships are still running with slide rules. Some of these are a bit too sentimental, some based on concepts that don't really resonate today, and the last, "Methuselah's Children", is pretty weak - 100,000 people surviving on a spaceship built for a much smaller number??? But the idea of framing a future history based on technological advance rather than, say, the mysticism of Olaf Stapedon remains engaging. In particular, the theocratic America of If This Goes On- is rather closer to the bone now than it was in the 1940s. The whole collection is one of those taproot texts of the genre that remains well worth reading.
This reached the top of three unread piles simultaneously; it was my top book acquired in 2016, my top unread sf book, and my top remaining book from your recommendations. Next in those lists respectively are The World of Yesterday by Stefan Zweig, The Island of Dr Moreau by H.G. Wells, and Hardwired by Walter Jon Williams.