This IS an important contribution to literary theory. The points that Lakoff and Turner make are very good, very logical, and will make you go "Of course! Why didn't I think of that?" It will not only change the way you read poetry, but will impact the way you watch t.v., listen to people speak, read the newspaper - any endeavor involving language. Why the low rating, then? Lakoff and Turner are structuralists, and they repeat everything over and over again, breaking things down to their minute building blocks. They made a very convincing argument in the first chapter, I thought, and didn't need to keep going the way they did. The third chapter, in which they apply their theory to a William Carlos Williams poem is also very good. Those two chapters would have sufficed. Again, an important book, but rather boring at times.

The important claim this book makes is that literary language does not differ from common everyday language. Poets make use of the same linguistic resources and cognitive mechanisms we all use in everyday situations. They just do it better, in innovative ways. The discussion of poems the authors provide to support their argument should perhaps be more articulate and systematic in order to be truly persuasive. At times one gets the impression that this book was conceived as a kind of divertissement in wait of future, more carefully planned incursions on the subject.
However, this does not diminish the importance of a book which urges literary critics and all those who like books to consider the cognitive basis of both everyday and literary communication. Also, More than Cool Reason can be read as an accessible introduction to Lakoff and Turner (and Johnson)'s theory of conceptual metaphor. For a much more articulate discussion, I would recommend Lakoff and Johnson's "Philosophy in the Flesh", but then you will have to draw the implications of their theories for literature by yourself.