For chapters 1, 3 and the conclusion alone, I'd give this book 5 stars, but sadly 2, 4 and 5 are a little tedious. That said, it'd be a great book for anyone who's interested in Dante, but hasn't read him, and I'm probably being overly harsh on chapter 2.
Chapter one sets out Auerbach's slightly odd philosophy of literary history in a highly condensed form. The essence of this is: literature can either present human beings as human beings, a combination of body and soul; or it can present them as merely one or the other. His preference is clearly the combination view, and that makes sense. Add to this some particularly dubious periodization (epic/tragic/Christ arrives! We care about the body!/dark ages (we forget the body)/Dante liberates us all! Yay!) and you have the general historical argument of the book.
I'm harsh on chapter 2 because it's about Dante's forebears and his early poetry, which is essentially coterie work. Historically important, yes. Worth 40-odd pages, not so much. Chapter 4 is a textbook account of the physical, ethical and historical/political theories that go into the Commedia, combined a little bit with the overall structure of the poem. It's good, it's just that you'll get the same knowledge by reading, um, the Commedia and a few of Hollander's notes thereto. Chapter 5 is a series of close readings of lines which spirals out of control into a kind of rapturous nineteenth-century praise criticism. Auerbach did much better in 'Mimesis.'
That leaves the great bits, chapter 3 and the conclusion, summed up I think in Auerbach's claim that Dante "transforms Being [i.e., scholastic philosophy and Christian theology] into experience." I don't so much recommend that you read chapter three of this book, as demand that you do so immediately. And then the conclusion, which tops off chapter 3 three nicely.
Two complaints: first, Auerbach's argument that Dante's greatness lies in his attention to and valorisation of individuality can't deal with the increasing abstraction of the Paradiso. He confronts this problem, and suggests that the saints and so on aren't as individualized because their stories are well known- the kind of ad hoc explanation that Auerbach rightly dismisses elsewhere. Second, he argues, correctly, that "the subject and doctrine of the Comedy are not incidental; they are the roots of its poetic beauty," but also suggests in his conclusion that the doctrine is dead and only the poetic beauty and vision of body+soul together remains. Maybe you could make those statements consistent, but it would be difficult at best. There's no need to say that the doctrine is dead, of course; we might not be Thomists, but a good number of people still possess an ideal of, say, a united world at peace, which isn't so much different.