I was lucky enough to meet Kyle at the Mormon History Association meeting a few weeks ago. I had corresponded with him previously and found him to be an open, sincere and generous scholar. The book reflects this.
The book is over 640 pages long (including the Preface) and includes abundant material that I hadn't seen before, even though I've studied quite a bit about William Smith myself. Of course, I've been focusing on 1842 Nauvoo, a section Kyle covers only briefly, so it was delightful for me to learn so much more about William Smith before and after 1842. [Kyle didn't pick up on William's involvement with the Times and Seasons, but no one else has, either. If anyone had, I wouldn't have had to write my book--and we would have dismissed the Mesoamerican theory a long time ago.]
Kyle does a great job documenting his sources, too. He includes very helpful photos and illustrations. His narrative style is enjoyable to read. All in all, an excellent book and a valuable contribution to Church history.