Planning Armageddon has largely been well-received by the historical community. Lambert's argument is that the Royal Navy identified that Britain, through its maritime power, had the capability to use economic warfare to destroy Germany at the outset of any war, at the cost of crashing the world economy. However, this was not popular within the British government as a whole. The Treasury and Foreign Office were opposed to it on practical grounds (crashing the world economy would not be good for Britain's own economy, nor its place in the world), while the War Office believed that the plan had little place for it. There were even elements within the Admiralty that were opposed to the policy. As such, the RN was forced into a less destructive policy of blockade, as well as more peripheral actions like the Gallipoli campaign. Lambert also covers the flaws of the early implementation of the British blockade, through to his ending point in 1916.

The book has received good reviews from a number of significant naval historians. Eric Grove, writing in the Royal United Services Institute Journal, describes the book as

a book of high-quality research and analysis, which is truly a landmark in the historiography of the First World War.

Similarly, N. A. M. Rodger (in the International Journal of Maritime History) described the book as 'deeply impressive', and based on a 'massive scope and depth' of research. Andrew Lambert (no relation), in War in History, stated that

Anyone writing about the development of British grand strategy, diplomacy, politics, civil–military relations and inter-service rivalries of this period will need to study this book. The resulting debate will affect how the First World War is understood, and how it lives in the present.

However, there has been criticism from several authors. Most of this focuses on Lambert's use of the relatively fragmentary sources in the Admiralty's archives, with the implication that he is reading too much into relatively limited information. Samuël Kruizinga, in the journal First World War Studies, suggests that

some aspects of Lambert's book may be suffering from exaggerated advertising or the author's over-interpretation of primary source material.

Other authors go further. Matthew Seligmann's article 'Naval History by Conspiracy Theory: The British Admiralty before the First World War and the Methodology of Revisionism' is, as the title suggests, highly critical of Lambert's methods. While it focuses on Lambert's other works (especially the concept of 'flotilla defence'), the criticisms it contains can also be levelled at Planning Armageddon. Seligmann charges that Lambert has a tendency to fill in gaps in the primary source record with his own theories and assumptions. There is certainly some merit to Seligmann's criticism, though it is, arguably, overstated. Other post-revisionist authors take more measured criticisms. David Morgan-Owen points out there is no definitive evidence for Lambert's arguments, and that a large amount of the Admiralty's effort had instead focused on more traditional methods of winning the war, in his article 'An ‘Intermediate Blockade’? British North Sea Strategy, 1912–1914'. In his book The Fear of Invasion, he also makes the point that Lambert had missed the need for the Allied armies to stave off defeat by land for long enough for the economic warfare strategy to take effect. Shawn Grimes, meanwhile, has shown that plans for amphibious operations against Germany were better developed than Lambert assumed.

The book is certainly worth reading; as a history of British economic policy and planning in the run-up to WWI it is almost unparalleled. It is worth keeping in mind the criticisms of the post-revisionists while reading it, though.