Retro-Hugos are given out at WorldCons held 50, 75, or 100 years after a WorldCon in which no hugo award was presented. The Retrospective Hugos were added in the 90s, but only awarded 3 times.
Here’s my opinion on three of the nominees for the 1939 Retro-Hugo for Best Novel:
Carson of Venus: An adventure book, a romp, and good fun, but I’m not sure if I felt it had enough substance on its own to compete for an award. It was also obviously serialized.
The Sword in the Stone: I wish I had had the chance to read this when I was a kid. I thought I had, but apparently not. Its whimsical story lines and celebration of imagination and play reminds me more of Peter Pan and Wendy than of any other books about the Merlin/King Arthur Legend.
Out of the Silent Planet:For a book about landing on an alien planet, there is an awful lot of philosophical moments. I dropped from 5 stars to 4 stars just because of the blatant moralizing.
And yet, I think that out of the three books I read, I would award Out of the Silent Planet the 1939 retro-hugo, although it is a close race with The Sword in the Stone.
And I still want to read that 1939 best novelette nominee, Pigeons from Hell.