This is one of the best books I have read in a while. I've read a few books about WW2, including Shirer's The Rise and Fall of the Third Reich, but this one is probably the most interesting. It has the advantage of being a contemporaneous account of Germany from just after the Nazi party took power to part way through the war. It is fascinating to read accounts of the big crisis of the day without hindsight to put them into a specific narrative.
It gives a wonderful feel for what it was like inside Germany before and during the war, while the populace both worshipped and feared Hitler as he consolidated his power in Germany and slowly exposed the weaknesses in the post WWI European order.
The only flaw in this fascinating book is that Shirer left Germany in December of 1940, so he never got to see and write about German reaction to Germany turning on it's ally, the Soviet Union, and opening the long dreaded Eastern front and to America being brought into the war by Japan's attack on Pearl Harbor.
Amazon Link: Berlin Diary: The Journal of a Foreign Correspondent, 1934-1941
