I think Feser‘s greatest success is in his arguments for a re-consideration of Aquinas’ Aristotelian metaphysical ideas, especially with regard to causation, but also with regard to an ontology of potency and action, and hylomorphic (form/matter) dualism.
My main criticism is that while Feser’s assumed role as Aquinas’ champion is usually a benefit to the reader, as Aquinas is presented in most sympathetic light, he is inclined to insist that all of Aquinas' ideas are equally meritorious. In some cases this leads him to present arguments which seem to go beyond what would have occurred to Thomas himself.
But, with plenty of references for further reading, Feser has given the reader a roadmap for further study to follow onto his fine introduction.
Below are somewhat scattershot notes and comments I made while reading the book. To briefly summarize my own views: I'm attracted to some of the metaphysical elements of Aquinas/Aristotle as they relate to causation and mind, and I'm even sympathetic to some of the cosmological arguments. On the other hand, I was unconvinced by significant parts of the Thomist package, including arguments by analogy for some of the divine attributes, God's nature as pure act and his separateness from matter, and the special nature of the human soul.