Throughout much of The Rise and Fall of the Third Reich, Shirer maintains an authoritative and more-or-less-detached tone that reflects his position as a journalist and an historian. It's a tone that we tend to associate with academic writing, in which authors typically maintain a certain intellectual distance from their subject matter.
Having said that, Shirer's tone throughout TRFTR can become bitterly scathing. His words can be sharp, cutting, and full of obvious disdain. Given his subject matter, it's not surprising. Here's a taste of his characteristic tendency to give free rein to his disgust as he describes Julius Streicher:
This depraved sadist, who started life as an elementary-school teacher, was one of the most disreputable men around Hitler from 1922 until 1939, when his star finally faded. A famous fornicator, as he boasted, who blackmailed even the husbands of women who were his mistresses, he made his fame and fortune as a blindly fanatical anti-Semite. (1.2.85)
Our favorite example? How about the description of Walther Funk not as funky, but as "a greasy, shifty-eyed, paunchy little man whose face always reminded this writer of a frog." (2.5.133)
There are lots of passages like this. Shirer loves to ridicule the personal appearance of people he can't stand, and he doesn't pull any punches when he feels people are deluded, sadistic, ignorant, or just plain bad actors.