Gribbin has written rather evocatively about the Multiverse idea in earlier books (one of the Schrödinger-titled ones, I’m fairly sure), and I picked this one up eagerly. Unfortunately, I didn’t like it half as much (and with my similar feelings about The Matter Myth, I may be about ready to give up on Gribbin—alas, for I loved some of his earlier works). In characteristic style it is full of colourful metaphors, but somehow they feel disconnected, and some of them leave me more puzzled than I was without them: For instance the suggestion that a “many similar books” view of the Multiverse is analagous to an Everett-style “branching” view is mystifying to me, since only the latter gives any hint of why worlds should be “related” and so be in any kind of position to interfere. Of course this is the danger of analogy—one may communicate to one person what it fails to communicate to others; one size does not fit all—but when his past books have seemed so useful to me, the failure of this one is disturbing.
It also comes off as a great deal more speculative than previous works, though it is perhaps difficult to identify precisely why: QM interpretations are, after all, pretty much all speculative in some regard! Maybe it is that they sound less like interpretations this time around than gospel truths (and for all I get from the explanations, they may as well be gospel—that is, unsubstantiated).
If you want an overview of Multiverse models, this may well be a good book for you (though maybe a sample of its bibliography would be better). If you want an explanation of QM and the Everett model, I can recommend Gribbin’s own earlier work, In Search of Schrödinger’s Cat. If you want explanations of other models, I don’t know what to recommend; perhaps not this one.