While there are "sympathetic" biographies in a good sense, like Robert K. Massie's new bio of Catherine the Great, there are sympathetic bios that aren't so good. And this is one of them.
It's not quite craptacular, but it's nowhere near a "critical" study. Written by a West Point grad, and, as one other reviewer notes, some sort of "authorized" bio, it's got enough of a suck-up attitude that it doesn't question him at all. (The type of people who blurb it on the back, starting with Tom Brokaw, also indicate the quasi suck-up nature.)
For example, did the "surge" in Iraq, combined with the Anbar Awakening, really work, in part, because a fair amount of Sunni ethnic cleansing had already played out, and in part because some awakeners were content to take some cold U.S. cash and bide their time? Author Paula Broadwell never asks these questions, either rhetorically or of her subject.
Nor does she address the questions of whether or not Petraeus is a "political general." (Short answer: Every general is, at least within the Army; career bird colonels are the ones who aren't.)
Also, given the subject matter, it's "interesting" that Broadwell apparently made no attempt to see if anybody would talk off the record about Afghanistan, or Iraq, issues. That goes in hand with a quasi-"approved" bio. Surely a two-star or three-star not in the Petraeus mentorship pipeline would have talked anonymously if Broadwell had wanted to pursue that angle.
Beyond that, it's bland in that we don't learn much new from this book. Pass. Wait 10 years, until he retires (I hope) from the CIA, and see if a real bio is out.