The book has one important attribute: it's clear, undoubtedly. Having a minimum of prerequisites, I think there's no way to not understand what Prof. Cohen says through its pages. It makes the job of learning this part of theory easier than any other text.
But ... but I can't totally agree with Cohen's crusade against formalism. I agree that the first target of a book should be to clearly transmit the intended knowledge, and Cohen perfectly succeeds in this. But formalism too has its importance, thereafter. A compact and clear formalism helps to communicate efficiently, and moreover unambiguously. Like in mathematics, the first, important thing is to understand. Yet, there's no way for you to efficiently work with math without using any kind of formalism, should it be more or less "standard".
That's it: a very powerful book for a "profound" understanding of the subject; a bit more of natural formalism would make it a "complete" understanding also, and the book a five stars one.