If you've read other accounts of the U.S. Civil War and want it in more detail, then this is the book for you. It took the author 20 years and over 3 million words to write this account. He tells the story in an interesting manner.
About the only area that I was disappointed in is that he doesn't talk very much about the causes of the war. Prior to the war, he follows the two eventual leaders (Lincoln and Davis) .. but does comparatively little to look at the broader landscape.
This is a minor point, though. It's an excellent account.