In my experience, there are four books that fundamentally explain why Germany lost the war; David Irving 'Hitler's War', 'Barbarossa: The German Campaign in Russia - Planning and Operations (1940-1942' by R.G. Grant, 'Mechanized Juggernaut or Military Anachronism: Horses and the German Army of World War II' by R.L. DiNardo, and 'Invasion 1940' by Derek Robinson.
Taken together they tell such a story of German incompetence, internal feuding, conflicting egos, its quite astonishing that the war lasted as long as it did. Hitler was forever vacillating, Goering crippled the Luftwaffe before it had even begun, Operation Sealion planning was a mess, etc. etc.
Invasion 1940 delivers far more than it promises. Dereck Robinson did his National Service as a radar plotter in the RAF, then went on to read History at University. He has a mind for the 'real' as opposed to myth, propaganda and the plain fanciful and an historian's eye for detail, objectivity and impartiality. Some of his information is quite astonishing in its significance for the whole war story. And yet he conveys it all with a certain sardonic wit that is well in keeping with his theme. A very readable and enjoyable work.
After reading Invasion 1940 and any of the other above mentioned works, you will begin to wonder how Germans came to have such a fearsome reputation for 'efficiency'. When Germans are angry, fed up and emotionally driven they can be just as mediocre, incompetent and muddle headed as anyone else. No wonder when others call them 'hard working' (fleissig) they sometimes burst out laughing. They are human after all. Invasion 1940 shows this very clearly, and helps to balance up the War Legend with a very welcomed dose of reality.