A somewhat ok overview of WWI. Based on other readings on the subject (Guns of August, Castles of Steel), I'm not sure that the author gets all of his facts/analysis right. For instance, when talking about a given battle or political decision, Guns of August might mention three different factors that contributed to the decision. Keegan's book will only mention one factor (and often the least important one).
Similarly, when it comes to the naval theatre, he outright disagrees with Castles of Steel, and I think incorrectly criticizes several of Fischer and Jellico's decisions. This was a bit galling for me, given the enormous experience and clarity of thought of these two men. For instance, Keegan snipes a lot at Fischer's decision to build battlecruisers (BCs) instead of more and more modern cruisers. Keegan says that the BCs intended roles were as scouts and to fight battleships directly, which isn't really the case.
The BCs could act as scouts, and they could support battleships against other battleships. Their main role though was hunting down and killing anything smaller than a battleship. Keegan then goes on to blame Coronel partly on the limited number of the expensive BCs, rather than on the miscommunications and political factors that led to the British commander choosing to engage in an unwinnable battle. Keegan also skips over the fact that once a BC did arrive on the scene, it did exactly what it was supposed to. The German ships couldn't out run it and couldn't fight it, and so were completely destroyed. Later on at Jutland, Keegan tries to support his point by implying that the British BC casualties were because the BCs tried to engage battleships directly. However, that wasn't actually the case, and the casualties were instead due to a BC vs BC fight. Finally, Keegan also I believe misses the point of Fischer's maxim about speed being the best defense. Fisher was not saying that speed allowed ships to avoid shells, but rather that it lets ships avoid unfavorable engagements in the first place.
Alright, one final point. Again at Jutland, Keegan criticizes Jellico's decision to turn his fleet away from the German torpedo spread. The criticism is basically that Jellico declined the chance to risk his fleet in order to win a major naval victory. Keegan misses out on or doesn't mention Jellico's reasoning that just by maintaining the fleet's strength and the blockade, the British fleet was already winning about 90% of what it could possibly win. Keegan doesn't draw the connection between Jellico preserving his ships (and power of blockade) and the collapse of Germany two years later, which in turn led to the scuttling of the entire German fleet.
So, based on the data points I do know, I'm not 100% confident in the analysis in the rest of the book. He does make several interesting points about the ground war, and it was relatively readable though, which is something.