Billions of years into the future, the universe is in the process of collapsing. Deyv, a member of a primitive tribe, ventures into the wilderness to find a wife. On the way, his soul egg, an object all people wear around their necks that is believed to house their souls, is stolen. He meets up with a girl who's egg was also stolen and a centaur-like plant man and they go on a quest to find the witch who ordered the thefts, only to be sent on a quest of their own upon finding her.
Dark is the Sun is a pretty good adventure story containing a lot of elements I like: crazy creatures, lost technology, and portals to other words. It also raises questions about religion and what it means to have a soul. Although I saw the ending coming, there were a lot of surprises along the way. The Shemibob or Freesh could have easily been one dimensional caricature villains but ended up being well rounded characters.
To sum up, this is a good science fantasy story and should appeal to fans of Philip Jose Farmer's other work, as well as those readers looking for a good adventure story.
Besides, where else are you going to find creatures that resemble boats and mate by shooting at each other with cannon-like organs?