I liked this book, had no problem reading it, and recommend it. Presumably when reviewers refer to it as "dry", they mean in comparison to such popular histories as Peter Hopkirk's fascinating "The Great Game". But, Hopkirk's point of view lends to the events an air of "the plucky British soldiers" fighting against "incredible odds" in their 19th century incursions into Afghanistan. What happened is that the disciplined British military with the aid of superior tactics and weaponry massacred numerous Afghanis in their quest to keep their Indian empire secure (from a Russian invasion that might never have occurred anyway), and, in due course, suffered some massacres of their own. I don't suggest Hopkirk whitewashed these events. Rather, he knows a story is more appealing with "heros" and "villains", and constructing these is how the very readable "The Great Game" makes a century of fairly detailed Central Asian history palatable.
Ewans's book lacks heros and villains. It's briefer and is consciously even-handed, written with a diplomat's grasp of how the personalities of leaders and the policies of powerful countries towards poor ones steer events. If you want a pithy review of Afghanistan's interactions with the world's great powers, its politics, and the succession of leaders from Dost Mohammed forward, this is your book. It certainly served me well.
Weaknesses of this book include, first, the sketchiness of the pre-19th century history and, second, a sharp focus on leaders and politics giving little idea of how ordinary Afghans lived, especially in rural areas (that is, until the closing chapters dealing with the Communist government, Soviet invasion, and regimes of the Mujahidin and Taliban). I'd like to know more about life in and leaders of the powerful rural tribes, who for 150 years have erected road blocks to the policies of kings, prime ministers, and presidents.
One source for conditions in the country-side are the travelogues of 20th century adventurers: Robert Byron "The road to Oxiana" (1930s - 6 stars out of a possible 5, though about 2/3s of that book concerns Iran), Eric Newby "A short walk in the Hindu Kush" (1950s - humor in the mountains), and Peter Levi "The light garden of the angel king" (1970s - next on my stack to read, but seems highly regarded by all).