I’ve never read the whole thing, although I heard an extended audiobook excerpt recently and thought it was OK. A bit dated. I know movingfinger was reading it a few years ago - you may want to ask him or her. I see, from searching for the words “Shirer” and “Reich,” that 4d3fect, Horatius and Ludovic have read it, too.
I’ve told this story here before: my sister once lent that book to a friend and, without looking closely at it, stuck in an old bookmark as she did so. The friend later called her, laughing, to report that the bookmark must have been in another, very different book before. My sister had written on it, “This has a wacky cast of characters and is pretty implausible at times, but I think you’ll get some laughs out of it.”
Here’s an old thread that may be of interest: Shirer's History of the Third Reich