As I promised in another thread, I went and bought Sorrow of Empire.
I picked it up last night and finished my reading it about 10:30 last night. Its a quick read, but I thought it was a great read. The additional material really adds to the original version.
I enjoyed watching Mack weave elements from the original Television series, as well as elements of other works into the novel. If I'd have to compare it to something else, I'd argue its like the Extended Editions of Lord of the Rings. The original story is great, but I think the expanded version really provides a greater expansiveness to the story.