I just read the novel!
I have to say, I can't believe how faithful the mini-series is to the book. As I was reading, I could remember each scene. I suppose there were a couple of city council meetings that may have been cut, but practically every critical scene was in the mini-series (another reason why I don't want to see a shortened version put on DVD).
A few differences:
1) I seem to remember more of Tess Harper's character (Will Henry's wife, Carrie) throughout the series and not so much in the novel.
2) More dialog from Brad Davis' Sonny Butts in the film (like the intense scene with his mother at the dinner table). Usually it's the opposite, but they seemed to enhance the character a bit more. Of course the more sexually explicit moments from the book (most featuring the Sonny Butts chapter) are understandably edited in the mini-series.
3) They changed a couple of names of certain characters. In the book Joshua Cole is actually Willie Cole (considering his best friend is Billy Lee, the Joshua/Billy relationship sounds a little better than the Willy/Billy relationship. Also, Billy Dee Williams' character is called Tyler Watts in the mini-series, but it's Tucker Watts in the book. I'm not sure why they changed that, but either name sounds fine. Finally, they changed Danny Glover's character from Marshall Parker (in the book) to Marshall Peters (in the movie). Very curious, but whatever.
4) I don't want to give away any spoilers but the big revelation between Tyler Watts and Billy Lee DOESN'T EVEN HAPPEN in the novel, if you can believe it. Instead the novel has a much more downbeat ending featuring Hugh Holmes. I have to say while it works for the novel, I'm extremely glad for that modification in the movie.
Anyway, it's a great read! And at least I have that until they finally release the whole darn mini-series on DVD.