The online magazine The Edge has a set of "hard questions" by experts and notables in a variety of fields, some of which discuss multiverse theories. http://www.edge.org/q2002/question.02_index.html.
Paul Davies critiques the multiverse+anthropic_principle explanation for what we see, in http://www.edge.org/q2002/q_davies2.html: Sir Martin raises the question of whether what we consider to be fundamental laws of physics are in fact merely local bylaws applicable to the universe we perceive. Implicit in this assumption is the fact that there are laws of some sort anyway. By definition, a law is a property of nature that is independent of time. We still need to explain why universes come with such time-independent lawlike features, even if a vast and random variety of laws is on offer. One might try to counter this by invoking an extreme version of the anthropic theory in which there are no laws, just chaos. The apparent day-by-day lawfulness of the universe would then itself be anthropically selected: if a crucial regularity of nature suddenly failed, observers would die and cease to observe. But this theory seems to be rather easily falsified. As Sir Martin points out, if a particular remarkable aspect of the laws is anthropically selected from a truly random set, then we would expect on statistical grounds the aspect concerned to be just sufficient to permit biological observers. Consider, then, the law of conservation of electric charge. At the atomic level, this law is implied by the assumed constancy of the fine-structure constant. (I shall sidestep recent claims that this number might vary over cosmological time scales.) Suppose there were no such fundamental law, and the unit of electric charge varied randomly from moment to moment? Would that be life-threatening? Not if the variations were small enough. The fine-structure constant affects atomic fine-structure, not gross structure, so that most chemical properties on which life as we know it depends are not very sensitive to the actual value of this number. In fact, the fine-structure constant is known to be constant to better than one part in a hundred million. A related quantity, the anamolous magnetic moment of the electron, is known to be constant to even greater accuracy. Variations several orders of magnitude larger than this would not render the universe hostile to carbon-based life. So the constancy of electric charge at the atomic level is an example of a regularity of nature far in excess of what is demanded by anthropic considerations. Even a multiverse theory that treated this regularity as a bylaw would need to explain why such a bylaw exists. It seems that this point can be addressed pretty well by the flavor of multiverse theories we consider here, in which "simple" universes are inherently more likely than more complex ones. In this model we would predict that the universe would be just as complex as necessary to support our kind of life, but no more so. For a constant to be stable to better than 1/100,000,000 is not that surprising; it is plausible that the simplest theory has that constant being absolutely stable. It would take more information to specify a formula for variation of some physical unit than to specify a single value which never varies. The "Sir Martin" article being responded to above is interesting in its own right, as an attempt to justify exploring the multiverse concept despite some complaints that it is metaphysics rather than physics. In http://www.edge.org/q2002/q_rees.html Martin Rees gives his own example of an apparent departure from simplicity: the fact that our universe seems to have a considerable portion of its mass in dark matter, which doesn't do anything obviously useful. Of course it may well be that dark matter plays an important role in the formation of galaxies, which allow for the formation of 2nd-generation stars which have enough heavy elements that they can have planets. Hal