On the side of cosmological argument, we begin with a substandard discussion of the first three Ways in Aquinas. Oppy accuses Aquinas of giving invalid arguments since the arguments clearly fail to establish the uniqueness of the First Cause (pp. 99, 103, 106). The accusation is ludicrous since Aquinas cannot be intending to establish uniqueness in Question 2 (the Five Ways) of the Prima Pars of the Summa Theologiae as he explicitly devotes Question 11 to arguing for uniqueness, and Oppy never considers the arguments of Question 11. On p. 101, Oppy speculates about how Aquinas might rule out the possibility of an endless regress of movers, apparently unaware of Aquinas' giving three explicit arguments in the Summa Contra Gentiles, I, 13. In fact, Oppy in general seems quite unaware of the fact that the arguments in the Summa Theologiae are mere summaries, and extended subarguments for the main premises of the Five Ways are given elsewhere. Nor is any use made of the distinction between per se and per accidens series which appears to many to be central to interpreting the text. Without addressing Aquinas' full argument, the comprehensiveness necessary for Oppy's project has not been achieved.
This sort of substandard treatment of Aquinas's arguments is appallingly common among atheists who discuss them, particularly when only a tiny bit of research could remedy these flaws. The uniqueness objection is especially absurd (and absurdly common), and comes from the ridiculous practice of treating arguments in a wholly decontextualized way. It is a travesty that it ever survives undergraduate philosophy courses.