I've thought about a few different ways William Lane Craig could frame his version of divine command theory, and each one seems to result in substantial problems.
- If goodness is metaphysically identical to sharing a likeness with God's essential nature, then aseity, necessity, immutability, omniscience and so on would be morally significant properties, as they are each instantiated within God's essential nature. But this is silly, I'm clearly not lacking in moral virtue or value because there are things I do not know! None of these divine properties that I mentioned are morally significant, and so this version of divine command theory must be false. Also, it's noteworthy that on this version of divine command theory and greatest being theology, God simply cannot be necessary for an objective morality. On greatest being theology God is defined as the greatest conceivable or possible being, and as a result God would have the greatest subset of great-making properties instantiated in his essential nature. But then goodness would just be a likeness to the greatest subset of great-making properties. Since God is defined as the greatest being, there must be some objective standard of greatness external to him or else the definition of God is just ill-formed and we fall into theological noncognitivism But if there is some objective standard of greatness external to God and the objective standard of goodness just turns out to supervene on greatness, then there must be an objective standard of goodness external to God! William Lane Craig (as well as practically every learned Christian) does ascribe to greatest being theology, and so this critique should be alone sufficient to refute his moral argument, assuming he really does wish to commit to this version of divine command theory.One more thing to note, this does seem to be the most popular view. It's very common for Christians to say that the property 'goodness' is identical to the property 'Godlikeness'; having a likeness to God; being like God. Clearly goodness can't be identical to God's whole nature, as it would include too much (every contingent choice he's made, every contingent property). No, if it's going to be God's nature at all then it has to be specifically his essential nature; or in other words the set of properties that are necessarily instantiated in him. Any more and divine command theory would fall apart, and any less would be arbitrary, thus prompting the question; "Why this subset of God's properties, and not another?".
- If goodness is metaphysically identical to sharing a likeness with God's dispositional properties, then divine command theory is a theory of moral virtue only, and fails to explain how there could be objective moral values. By dispositional properties I mean properties like; "If God were in the position to love others, then he would", in other words that God has a disposition towards loving others. And so on this view all good things are dispositions towards certain actions, but not the actions themselves or more broadly bare states of affairs. We cannot say that loving others or a state of affairs involving love is a good thing, but rather having the disposition towards loving others; being the sort of person who would love others given the opportunity. In this case divine command theory must either not tell the whole story of moral ontology, or there must not be any morally valuable actions or states of affairs, but rather only morally valuable dispositions towards actions or states of affairs; virtues. But in that case a very strong logical problem of evil argument could be formed, as good dispositions do not require evil in the same way good actions or states of affairs might. And because of this, God could have produced a creation at least as good (though probably much greater) than the actual one, all without permitting any evil.
- If goodness is metaphysically identical to sharing a likeness with the sort of actions God would be disposed towards performing, or states of affairs God would be disposed towards preserving or obtaining, then immediately divine command theory fails to be an inherently theistic account of moral ontology. On this view an action is good just in case, were God to be in a position to perform that action, he would. The atheist can very consistently reject that God exists, and yet affirm that if God were to exist and be in a position to love others, then he would indeed love others. And thus on this form of divine command theory, the atheist can very consistently believe that love is good. In fact it's even worse; goodness isn't being metaphysically identified with any feature of God at all. The property of being the sort of action God would perform were he to be in a position to can be instantiated even in a world in which God himself does not exist. But if goodness can exist in the absence of God, clearly it's not identical to God in any way.
I can't imagine any other way to form divine command theory that wouldn't just get too implausible, so I suppose these are some serious issues that any divine command theorist would have to answer to.