If I hadn't seen the miniseries I'm not sure how I would have felt about the book, because it's hard to keep track of all of the names in the book without a face to put them with. The series follows the book very accurately, even the parts that I figured they put in to spice it up were in the book as well. The book did include more details though, including their record-setting 3 day march to Atlanta (I think?).
In short, they're both great.