Good grief, this was huge!!
I lost interest sometime in 1942, and skipped ahead to the part I wanted to read: the 1944 NW Europe campaign. There is where the author did good work in analyzing the workings (or not) of SHAEF and General Smith. Unfortunately, it seemed like there were two books here (at least), and the one that was the biography of Smith was way overshadowed.
I had difficulty whenever the book tried to cover the snarled lines of supply that bedeviled the Allies in 1944. The author may have been as confused as I was, because I could not make heads or tails of what the problem was, what the suggested solution was, or what the results were. I did gather that Eisenhower didn't want to make a hard decision, and so left a lot of things lie.
The Eisenhower that emerges here, by the way, is a very different one than I have sometimes read, but agrees with other detractors. As I said above, he tried to avoid hard decisions, and preferred to hide behind woolly memos that weren't really orders.