I don't think there can be much more to add to reviews of this book across the internet. It is pretty much a step-by-step of the long and aggravated war that Edward III incited chasing the crown of France, and though extraordinarily in-depth, is one of the easiest reads on the subject you'll likely find that is factual. Sumption does a great job of keeping on topic as well, which means anyone looking to books for a wider understanding of medieval society will unlikely find it, which to me is a bonus. Many books can waver on certain topics too long or not enough when they are broader subjects. This keep well on track, and right in the action.
Personally, I'm researching for a novel, but anyone remotely interested in how these battles were won, who was there and what they did (and what weapons they used), this is for you. It also introduces some interesting insights into weaponry of the era in motion, especially the victory at Crecy, one of the most revered historical battles, which changed everything, but didn't really gain anything.
Currently there are four books in the series, with the final one ending with the English expelled from France just before turning on themselves with the Wars of the Roses.