I realised that I have already written up two of the three winners of the retro-Hugos for Best Novel (here and here); this completes the set, having won in 2001 against Asimov's Pebble in the Sky, C.S. Lewis's The Lion, The Witch and the Wardrobe, E.E. 'Doc' Smith's First Lensman and Jack Vance's The Dying Earth, in that order. I've read them all except, oddly, the Asimov, and would certainly have voted for the Vance (incidentally the only author still living either today or in 2001 when the award was made). But my tastes are peculiar.
Farmer in the Sky is what would now be called a YA novel a juvenile (thanks, fjm), with our narrator, his father, his stepmother and her daughter leaving Earth to build a new colony on Ganymede. There is a significant amount of product placement for the scouting movement, which is not surprising as it was originally serialised in a scouts magazine. We encounter nice guys and nasty guys, and even a few women, though they don't get to speak much. There is a major natural disaster which wipes out two thirds of the colony, but our hero and most of his family survive. At the end of the book, our hero discovers some alien technology which incidentally saves his life.
A lot of this was already pretty standard sfnal fare even in 1950, but Heinlein fuses it all together into a coherent and literate package, which has a colossal amount of sensawunda, sufficient to keep the book going at full pace to thend and to keep its reputation alive among fans for decades. (He even manages the pro-scouting propaganda fairly discreetly, though of course this also helps underpin the gender and racial constraints of the narrative.)