Here is what Feser said:
Law's argument evidently presupposes a "theistic personalist" or "neo-theist" notion of God and is therefore completely irrelevant to the classical theism of Athanasius, Augustine, Anselm, Aquinas, et al., according to which God is not "good" in the way a human being is good, as if He and we both instantiated the same property; rather, He just is Goodness Itself, and anything less than that is (for a classical theist) necessarily other than God. Hence it is incoherent to suggest that God might be evil.
Re: the analysis of evil as a privation, I would say that it is hard to makes sense of individual examples of evil on any other view, and hard to make sense of evil as an objective feature of the world at all -- which the atheist himself has to do if he's going to make arguments from evil stick -- except on the privation view. I would also say that the privation view naturally falls out as a consequence of a general classical realist metaphysics (whether Platonist or Aristotelian). In any event, whether the classical theist can argue for this analysis of evil to Law's satisfaction or not is irrelevant to the question at hand, because the analysis is integral to the classical theistic view of God and the world. Thus, if Law says that there might at least in principle be a (classical theist) God who is evil, then he either doesn't understand what classical theism means by "God" or is just begging the question against classical theism. Either way, as I say, his argument is irrelevant.
Now, a critic might at this point say that he isn't familiar with and doesn't understand all this stuff about evil as privation, God as pure act, God as Goodness Itself, etc. But if so, then that's the critic's problem, because in that case he doesn't understand classical theism itself and therefore shouldn't presume that he has raised any challenge to it.
See, this is what annoys the hell out of me: The sort of atheist -- and this is the typical atheist, in fact -- who (if he is even aware of them in the first place) treats concepts like pure act, evil as privation, divine simplicity, the transcendentals, the distinction between per se and accidentally ordered causes, and all the other elements of the classical theistic tradition as if they were a bunch of oddities which the theist brings in in an an hoc way in order to patch up arguments that would otherwise have to be admitted to have been demolished by atheist criticisms; and as if he is under no obligation to try to understand them before judging that the traditional arguments fail. One wants to say: "No, dummy, these elements have always been integral to the tradition of philosophical theology, and if you don't know of or understand them, that only shows that you don't have the first clue about that tradition itself, and thus shouldn't be opening your mouth up about it." Which is, of course, what I often do say.
Accordingly, most atheist arguments, even most of those presented by otherwise serious philosophers (rather than by the Dawkinses of the world), are simply irrelevant to the question of whether classical theism is true. In fairness, though, too many contemporary religious apologists and Christian philosophers of religion have little more knowledge of the classical theist tradition than the typical atheist does. They argue for what is in effect (and whether they realize this or not) a decadent "theistic personalist" or "neo-theist" conception of God, and thus open themselves up to arguments like Law's. But that only shows that, here as in so many other ways, we modern Christians are inferior to our forebears, and are paying the price for forgetting the tradition they tried to pass on to us, and have passed on to us if only we'd listen to them. It doesn't show that there is anything wrong with the tradition itself. And the sooner we re-learn that tradition, the better.