A review by joshebarry
Forty Thousand in Gehenna, by C.J. Cherryh

adventurous dark informative mysterious sad tense medium-paced
  • Plot- or character-driven? A mix
  • Strong character development? Yes
  • Loveable characters? Yes
  • Diverse cast of characters? Yes
  • Flaws of characters a main focus? Yes

4.0

A great book by Cherryh that tells the story of a colony collapse, and explored the fascinating subsequent development and evolution of the human population in hand with an alien (intelligent) species named the Caliban.
Cleverly spread over ~400 years, the book allows you to see every step along the way, with some major theme changes throughout. The start, dealing with the collapse, is rather dark and depressing at times, while later sections are more hopefully. 
The book also is littered throughout with communiques and memos sent between the scientific research mission, which was a genus method of showing external points of view. 

Perhaps the best book I've ever read dealing with first contact, and one of the first that didn't fall into the cliche of 'the aliens are super clever and learn English so our readers can understand'. Having the Caliban communicate through body language and signs, as well as physical diagrams, made them as bizzare and unknowable to the reader as they are to the characters.