That's a decent link that provides a summary of the book.
Let's say I were trying to understand media, would the theories on that book provide more light than a poem by Dylan Thomas? ( These questions become more rhetorical with every iteration.)
Let's take the notion of "The medium is the message." If so then watching a hundred hours consisting of boxing matches should have the same effect of watching a hundred hours consisting of PBS documentaries. In my experience the results are significantly different.