After his previous books such as Stalingrad and Berlin, I was disappointed in this one. Other reviewers have covered much of what I would say - particularly how kind in general it is to both the US and France. It doesn't seem to add anything much to what is already known. I'd add that alarm bells rang when I read the chapter on Omaha. As this was written very recently, I expected it to contain highly relevant information found about 6 or 7 years ago regarding the deployment of the DD tanks at Omaha - and why they nearly all sank (the Anglo-phobic US Commander at Omaha ignored the RN instructions to send them in at an angle to the beach, the direction of the waves, and sent them head on - which is why they, and other vessels were swamped - a fact discovered by marine archaeologists diving on the tanks.)
There is also a tendency (though this is by no means unique to this author), to make judgements purely with the benefit of hindsight. For instance, he will heavily criticise the British for not advancing on an area vacated by German troops (usually during the night), when there is no way they could have known about this. Or there will be harsh critisism of an advance into a heavily defended area - which the day before hadn't been, but again, enemy troops had moved in during the night. The author seems to fail to appreciate that intelligence and communications of the day were not even close to the standards of today, but still judges the actions of military commanders as if they were, which is more than a little unfair. I also caught a couple of occasions when he contradicted himself - saying one thing, then later in the book showing this to be wrong (or misleading through over-generalisation).
The other, more minor (in the overall context of the book) criticism relates to his comments and treatment of France. It is apparent that the author knows little about Occupied and Vichy France between 1940-44 (and there is nothing in the bibliography to suggest otherwise), and has largely accepted the post-war mythology created by the French, which has now been thoroughly discredited.
Worth reading as an introduction, as it is very readable (although I found it a bit confusing determining who was doing what - country-wise), but like others, I would strongly advise looking at some of the other books mentioned by other reviewers. Not recommended if you're already familiar with the subject, as you'll spend too much energy fault-finding!