I had not heard of this book until I decided I wanted to read through the SF Masterworks list. Boy am I glad I did. I am amazed that someone in 1930 could write this story.
In this novel Stapledon gives the history of the human race from the near future to the end 2 billion years in the future covering the 1st men through the 18th men. His story is told as a historical narrative narrated by a future man, a man of the 18th men. There are no characters save all of mankind. The history tells about the rise and fall of many civilizations and even goes into genetic manipulation, super-brains, hive minds and one species of man with the power of flight.
If you are expecting a space-faring adventure with alien antagonists or man expanding through the universe, this is not it. In this story mankind is limited to our little blue marble until close to the end of the story. Then due to destructive forces in the universe mankind seeds Venus then Neptune.
Sometimes the prose in this book can be a little hard to get through (it was written in 1930 after all) but with that the scope and breadth of the story is amazing. Highly recommended!