Graham Oppy is one atheist philosopher of religion who is usually mentioned with great respect. In fact, I myself generally have a high opinion of Oppy's work, at least on ontological arguments.
The third chapter of Oppy's Arguing About Gods discusses the cosmological argument. Oppy's treatment of the subject is much better than that of Graham Priest or Nicholas Everitt, to say nothing of the Dawkins-Dennett crowd. Oppy sets out a pretty fair summary of the argument on page 100:
1. Some things are caused.2. Things do not cause themselves.3. There are no circles of causes.4. There are no inﬁnite regresses of causes.5. (Hence) There are ﬁrst causes.6. There is no more than one ﬁrst cause.7. (Hence) There is exactly one ﬁrst cause.
Oppy then goes on to question the truth of the premises, without giving the reader any hint of the arguments used to establish these premises.
Alexander Pruss, in his NDPR review, said it better than I can:
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.
I don't mean to bash Oppy. I think he is a very fair and careful philosopher. I would even say he's one of the better philosophers of religion out there. But the fact that one of the better philosophers of religion doesn't know his way around Aquinas' cosmological argument (or the work that's been done in its defense over the centuries) says a lot about the state of analytic philosophy of religion. Oppy was trained as a philosopher of language. Perhaps it's just the nature of analytically trained philosopher to be weak on any argument older than a century.