This book covers Bowie's family history and early life in great (sometimes exhaustive) detail and follows his career up until his appearance at Live Aid in 1985. It has been used as a source by other writers on Bowie, including Nicholas Pegg in his excellent 'The Complete David Bowie' and, whilst Bowie himself didn't participate in or approve of the book, the Gillmans interviewed approximately 150 people in preparation.
Peter & Leni Gillman's research is also extremely thorough and they provide factual (and counterfactual) information ranging from the details of Bowie's schooling and where he was brought up, through to specific details of the financial extravagance of the MainMan years and of the settlement reached between Bowie and his erstwhile manager Tony Defries.
The most questionable aspect, which also happens to be the book's central theme, is the insistance on the significance on Bowie of his half-brother Terry's mental illness. In support of this theory the Gillmans seek, sometimes in a rather contrived way, to link Bowie's lyrics (which they don't always transcribe correctly) and artistic decisions to Terry, which might be a good literary device but, overall, is less than convincing.
The Gillman's are also, to some extent, the victims of contemporary views on mental illness, and frequently fall into the traps waiting for any amateur psychologist, finding significance where they wish to in order to support their theory and expressing fuzzy or fashionable views about pschology as if they are facts.
The high incidence of mental illness in Bowie's family, it's implied, is likely to be hereditary, afflicting Bowie who is presented as being largely in denial. The alternative view is that Bowie's family, typically of British families of this period, was unable to express its distress and anxiety, was unable and emotionally unprepared to cope with the disruptions of war, unplanned pregnancies, poverty, and suffered as a consequence affective disorders unconnected to heredity.
The Gillmans suggest, oddly, that Bowie's success in removing himself from this mire consequently makes him responsible for all those in his family who didn't, and that his failure to become some sort of grand patriach is evidence both of his selfishness and his fear of madness.
Bowie's personal psychological crises it could be argued, were more likely due to the strain brought by fame and fortune of a level that had been previously unimaginable (but was commonplace for musicians of this generation including for example Led Zeppelin, Jimi Hendrix, John Lennon) and massively exacerbated by his consumption of drugs.
That Bowie is susceptible to fantasy & exageration in regard to his past seems only an example of his febrile imagination - the mistake made by the Gillmans is the failure to separate the artist from his art (was Shakespeare writing biographically in the Sonnets - probably not).
Otherwise the book presents balanced portraits of many of those close to Bowie (some of whom, including Angie Bowie, who were clearly unbalanced), gives a well written account of Bowie's life, and provides illuminating detail which a more mainstream biography might have skipped.