This history of the Luftwaffe was first published in 1967. Much research has been done since then, and our understanding of some areas has changed, but the overall picture is still accurate.
Killen tends to underplay the effectiveness of the Stuka, focusing more on its vulnerability during the Battle of Britain than its effective performance in the west in 1940, Crete in 1941 or during the early periods of the war in Russia, or later as a tank destroyer. For me he also overplays the weakness of the Luftwaffe - as an example he is rather scathing about the aircraft available to the Germans in 1939, but the German medium bombers he condemns were just as effective as their British or French opponents. It was only later on the war, when the Germans were struggling on with the early war types while the RAF and USAAF had introduced a new generation of heavier bombers and improved fighters that the German types begin to look outdated (not to mention outnumbered due to the massive increase in American military production).
Killen does a good job of tracing the pre-war development of German air power, in particular the pre-Nazi period when so many of the wartime companies produced the aircraft used by the 1930s Luftwaffe. There is also a good section on the airship, ending with the Hindenburg disaster (I'm always amazed that two thirds of the passengers and crew on the Hindenburg survived).
The author is also good on the failure to develop a new generation of weapons in the mid-war period, when aircraft like the Bf 109, Me 110, the Stuka and the He 111 were forced to fly on despite being past their peak, and the frustration of the Luftwaffe leaders who saw new designs appear too late or prove to be disappointing when they did take to the air (Messerschmitt's attempts to replace the Bf 109 are best the best example of this, although they only get a brief mention).
He is also good on the personalities of the Luftwaffe, including Goering, Udet and Milch, tracing their role in the rise and fall of the Luftwaffe and acknowledging their strengths as well as their weaknesses (even for Goering, who is often portrayed as an entirely broken reed after 1941).
Overall this is a good readable account of the rise and fall of the Luftwaffe that covers all of the main fronts on which it fought, and examines the reasons for the eventual failure as well as providing a readable narrative.
1 - Aircraft and Aces: 1914-1916
2 - Year of Attrition: 1917
3 - The Broken Wings: 1918
4 - Phoenix Rising: 1918-1926
5 - Awaiting Events; 1926-1933
6 - Air Force in Embryo: 1933-1935
7 - Into the Arena: Spain, 1936
8 - The End of the Airships: 1936
9 - Austria to Poland: 1938-1939
10 - Blitzkrieg! Poland, 1939
11 - The Battering Ram: France, 1940
12 - A Fortress Besieged: The Battle of Britain
13 - Heinkels Over London: September 1940
14 - Sunshine and Slaughter: Crete, 1941
15 - Red Star Burning: Russia, 1941
16 - The Unconquerable Island: Malta, 1942
17 - Airlift to Disaster: Stalingrad, 1943
18 - 'You can call me Meir!' Cologne, 1943
19 - Bombing Round the Clock: 1943
20 - Disintegration: 1944
21 - Fighters, Bombers or Fighter-Bombers? 1944
22 - Dresden and Berlin: 1945
23 - Cry Havoc to the End: May 1945
Author: John Killen
Publisher: Pen & Sword Aviation
Year: 2013 edition of 1967 original