It's probably tempting to dismiss this book as "New Age" claptrap. That would be a mistake.
In fact Dossey is highly critical of the "New Age" movement. And despite some overblown cover blurbs, he doesn't claim to have "proven" anything about the power of prayer in healing; he's making suggestions and exploring possibilities, not laying down law.
Nor, for the most part, is his speculation wild or unfounded. His suggestions are founded on two things: empirical research that seems to show prayer is effective in promoting the biological growth of certain forms of life under controlled laboratory conditions, and the theological/philosophical view that reality is ultimately a single, universal, "nonlocal" Absolute Mind.
However controversial these foundations might be, he presents his suggestions with proper caution. And he is especially careful to avoid falling into the New Age blame-the-patient trap; he is well aware that prayer doesn't always achieve the results we might like and that this isn't because somebody has done something to "choose" or "deserve" ill health.
On the contrary, he has a healthy sense that prayer is really (though this language isn't quite his) for the purpose of adjusting us to the Divine Will rather than vice-versa. (Anthony de Mello tells a story somewhere about a man who said, "In your country it is regarded as a miracle when God does the will of a human being. In my country it is regarded as a miracle when a human being does the will of God.") On his view, the "power" of prayer is shown as much in our acceptance of our health limitations as in their elimination.
There are a couple of places where Dossey threatens to wander off the deep end (e.g. his suggestion that prayer can change the past), and there's a little bit of language (e.g. "Era I, Era II, and Era III") that recalls bad 1970s self-help books. But I really have only one bone to pick with Dossey: he tends at times to overstate the difference between his views and those of traditional, "classical" theism.
There is a tendency among those (of whom I am one, which is in part how I know this) who left their childhood religions in their early teens to assume, more or less unconsciously, that our understanding of such religion was complete at that time and none of its adherents understood any of the cool things we went on to discover for ourselves. It's hard to shake one's implicit belief that those hidebound "fundamentalists" couldn't _possibly_ have known any of this nifty "spirituality" stuff; "dogmatic" religion is, of course, the arch-enemy of "true" spirituality -- isn't it?
Dossey has a very mild tendency in this direction. In consequence I suspect he will occasionally leave more traditional religious believers with the sense that they are being misunderstood, patronized, or both.
But it doesn't happen very often, and it hardly happens at all in this book. On the whole, Dossey's approach tends to confirm rather than undermine the great theistic religions' view of prayer.