One critic who has taken exception to Metaxas' piece is atheistic physicist Laurence Krauss. He wrote a letter to the WSJ which Daniel Bakken at Evolution News and Views excerpts and to which he offers a cogent reply.
Philosopher V.J. Torley has a lengthier and more thorough response to another of Metaxas' critics, Catholic philosopher Francis Beckwith, at Uncommon Descent.
In the course of his critique of Beckwith Torley quotes writer Damon Linker who contends that even if Eric Metaxas’ argument were valid, it doesn’t prove the existence of a God who loves us, let alone the God of the Bible. Says Linker:
...[N]atural theology doesn’t demonstrate the existence of the God of the Bible....Even if we consider it reasonable to speculate about the possible, mysterious role played by some form of divine intelligence on the origin of life, that provides not one ounce of support for the detailed, specific stories of divine revelation laid out in the pages of scripture. The God of the philosophers (and the scientists) is not the God of the Bible. At least not obviously or inevitably. And no new piece of scientific evidence is likely to change that.Linker is technically correct, of course, but it's a little difficult to place much weight upon his objection. To see why, imagine for a moment that it were established with a high degree of probability that the universe is in fact the work of an intelligent agent. What might we reasonably conclude about the nature of that agent?
Surely we could conclude that the agent is transcendent, i.e. it's not itself the universe - not material nor temporal - but is rather the being which fashioned the physico-spatio-temporal manifold and that it did so out of nothing since the material universe came into being, according to most cosmologists, ex nihilo (i.e.out of nothing).
We could also conclude that this being must be both unimaginably powerful and incomprehensibly intelligent. Since it transcends time it might also be eternal. Since it transcends space it's not limited by space. Moreover, since it has created, either directly or indirectly, personal beings with a sense of morality, justice, beauty and humor, it's reasonable to believe that it itself is personal and either possesses the aforenamed qualities or at least understands how they operate and "feel."
Finally, since it is the being upon which the contingent universe depends it's reasonable to think that this being has the property of being self-existent, not dependent on anything else for its own existence, otherwise we're faced with the absurdity of an infinite regress of creators.
Now all this may not add up to the God of traditional Christian theism, but it's pretty close. In other words, once it's admitted that the universe was created it's not a big leap to to the belief that the creator possesses many of the qualities of the God of Christianity. Thus, although a compelling argument for a cosmic designer does not amount to a knockdown proof that God exists, that's not what's important or significant about the argument. What's significant is that it provides rational justification for the theist's belief that God exists.
Indeed, it's also warrant for believing that theism is more rational than atheism. After all, the rational course is always to believe what's more probable than what's less probable, and the fine-tuning of the universe that Metaxas talks about is certainly more (epistemically) probable given that theism is true than it is given that naturalism is true. Put differently, intentional agency is a much better explanation for cosmic fine-tuning than is blind chance.