The best work I can recommend off the top of my head is probably James S. Corum,
The Roots of Blitzkrieg: Hans von Seeckt and German Military Reform, (University Press of Kansas, 1992). Okay, yes, it's not strictly Second World War (he deals with the interwar period and touches on the early campaigns), but it does give you a strong grounding in interwar German thought, how it evolved from traditional German (or more aptly, Prussian) thinking, and how it led to the Wehrmacht you see in the Second World War.
Another interesting piece is Weichong Ong, 'Blitzkrieg: Revolution or Evolution?',
RUSI, (Vol. 152, No. 6, 2007), pg82-7. Though brief, like most RUSI articles, Ong's piece puts an interesting focus on the longterm root of German thinking. IIRC the conclusion was that 'blitzkrieg', if even a doctrine at all, was the natural evolution of German military thinking dating back to the post-Napoleonic reforms of the Prussian army. This being particularly true of the Polish and French campaigns.
On strategy as a whole I can't recommend much without looking through some stuff. I did find a US Air War College article with some quick googling, looking at the subject through a bombing perspective. However, I wont vouch for it as I haven't the time to read it even briefly and the quality of this sort of thing (military-academic stuff by serving officers) can often be somewhat dubious.
Link to download here:
www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA397297
