This science fiction novel was published in 1971 and won the Hugo award in 1972. Farmer went on to write several other novels set in the same Riverworld, a planet that has been terraformed into one extensive river valley. Although it has its faults and is dated, it's still an excellent novel and essential reading for a science fiction fan.
Riverworld is a skilled novel that mingles history and science fiction. The main protagonist of the novel is Sir Richard Francis Burton, a fascinating historical figure who was a skilled linguist, explorer, and translator (he translated 1,000 Arabian Nights and the Kama Sutra, for example). He spoke 29 languages, an ability that comes in useful. The book opens with Richard Burton dying as an old man and then waking up on a strange, other world. He and the others around him now inhabit 25 year old, hairless, unblemished bodies in the peak of health and vitality.
The people around him are from all different periods and are people fairly well-known, such as Alice Liddell Hargreaves (the child Lewis Carroll interacted with as a child and probably based his books off of) and Hermann Göring (a Nazi War criminal). Another prominent figure is a man from "the future" of 2008 called Peter Jairus Frigate (and I realized after reading the Riverworld wiki that he has the same initials as Farmer and evidently is like him in several ways).
The story follows Burton and his gang as they explore the vast river valley and try to discover answers--are they in heaven, or hell, or something else? I loved the situation because it is sort of how I imagined the afterlife when I was a little girl--we would be reincarnated somewhere else on another planet. It is also an insight into the nature of humanity and what we would do if we started over in a world where there is no aging, no death, and no birth. If a person dies on the Riverworld, they are reincarnated and wake up somewhere else. They can obtain food and recreational drugs from mysterious contraptions around their wrists called grails and special sites called grailstones. Some of the people reincarnated on this world were horrible people during their lives, such as Göring, but even he changes in this new world.
While overall I highly enjoyed the book, I had some gripes with it as well. I wouldn't say it's sexist, per se, but some aspects of the way women are portrayed raised my hackles. The men's nude bodies are rarely mentioned but the women's are always mentioned when a female character is introduced. At one point Burton says of Alice Hargreaves to the effect that "she is only, after all, what men have made her" when ruminating about her Victorian uptight morality. Perhaps it is because we are following Burton's viewpoints. But aside from that niggling feature, it's an amazing novel that explores the nature of humanity.