Bound by necessity to start with the evident, I must say that Hume's Enquiry constitutes indeed a display of philosophical genius. Definitely a far more mature work than his Treatise on Human Nature (of which the reading I nevertheless do recommend), its principal qualities are its rigor of structure, the solidity of its arguments and the eloquent style through which Hume captivates the reader in such a way that the density of content is hardly perceptible.
Yet beware, as even though the style is to be revered, in the domain of philosophy it is the quality of content that constitutes the main criterion for judging a text. Yet neither in this sphere does Hume leave anything to be desired.
The leading thread of the argumentation is Hume's conception of the process of knowledge acquisition, but all through the book you'll find passages dealing with a variety of topics, from "writing theory" to 18th century theology and ethical debates.
On the first section Hume distinguishes between two types of philosophy, the distinction of which is based more on the style that characterises each of them and to the public they are addressed to than on their content.
The sections from two to five present a concise presentation of Hume's empiricist conception of the process of learning, which owes much to Locke's views on the topic (see Locke, an Essay Concerning Human Understanding) but can be said to constitute an "improvement" on his predecessor's thought.
Sections six to nine also deal with Hume's conception of learning and human knowledge, but this part differs from the previous one (sections two to five) in that it no longer consists on an explanation of the process of acquisition of knowledge, but rather of the consequences of this process. Put in a different way, sections two to five are a presentation of the genealogy of human knowledge, while sections six to nine deal more with the implications of such a genealogy. Sections ten and eleven are a presentation of the idea that religion and religious beliefs are not rational. This part has the aim not of discrediting religion, but rather of showing that it cannot be founded on reason, only on faith, and so that reasonable knowledge cannot be founded in religion, but only in reason and matter of fact.
Finally, section twelve is a presentation of the kind of scepticism to which Hume adheres on the basis of his conception of human knowledge and its boundaries.
As I said, to Hume's text I give five stars, but to edition itself I'm tempted to give three. I actually hesitate between three and four. The actual physical book is wonderful: excellent paper and ink quality, very nice typography, extremely useful numbering of the paragraphs (for those who really want to explore the text and its internal structure and articulations).
My main problem is actually that Oxford University Press of course a prestigious editing house, so I expected the most brilliant and enlightening notes, and was hence somewhat deceived (but should I give it only three stars simply because it being Oxford my expectations were higher than they would have been had it been published by a smaller editing house? -I'm tempted to say yes.
Do not get me wrong, its not that the notes are entirely useless, but they are somewhat basic to readers with a philosophical formation (even a basic one, as mine is), and some of the notes are even there only to explain the meaning of non-philosophical terms that even I, as a non-native English speaker, could understand.
Nevertheless, and on a more positive note, it does have an extensive introduction that, though somewhat basic, can still be useful. Thus I reconsider and change my mind. I give the text 5 stars. To the Oxford Edition, in terms of content 4 stars, and in terms of material/physical quality 5 stars.