I'll withhold judgement but looking at the advertisement for the Herspring book, it looked like just one more anti-Bush screed. I strove mightily to be balanced and objective in mine.
It's more like an anti-Rumsfeld screed. Sources are mostly MSM and personal interviews. I do not detect a conscious effort on his part to be very objective, but he's not extremely biased either given that his thesis - Rumsfeld was a very bad SECDEF - is not that controversial. What's interesting as it relates to this thread is that Feith is the only character in the book that comes out worse than Rumsfeld