This book feels more like a course than a textbook. The text reads like what a professor would tell you at the classroom, except it's in book form and accessible to everyone.
On a side note, considering the time this book was published, its 'Biographical Notes' section felt like a journey back in time. Only the birth dates of authors such as Sherwood Anderson, Ernest Hemingway, and Flannery O'connor were mentioned, without dates of decease.
It took me over a year to read this, for some reason. Probably because it's basically a large collection of short stories, and I tend to lose momentum with successive short stories.
I wouldn't say this is a good guide to understanding fiction. Rather, it's a collection of pieces with some interpretive notes, not a framework for analysis. I was left somewhat disappointed when that became apparent.
Still, it's a collection of great stories, with a lot of variety.
Worth the commentary on "House of Usher" and its critique of modern horror as a genre.
"The horror is relatively meaningless—it is generated for its own sake; and one is inclined to feel that Poe's interest in the story was a morbid interest."
Wilson's commented on this notion as a type of spiritual "catharsis" on his blog.
I enjoyed the variety in Understanding Poetry more than this book, but Cleanth Brooks provides an excellent introduction to literary criticism of novels through this work.
If nothing else, this is a superb collection of short stories, well worth your time even if the academic interludes are trying to some, they can be skipped and this book would still be a winner.