FANTASTIC book. This will be a classic, and it's a deep, mature complement as well as retelling of the story of Huck Finn. 

Told from the perspective of Jim, the slave in Huck's story, this is a powerful illustration and takedown of pre-Civil War slavery with heavy doses of philosophy and ethics and sociology. 

This book should be read and discussed in high school and college lit programs. Highly recommend to every one as a real eye-opener.

I also loved reading this via audiobook.