As a long time environmental activist and graduate student in philosophy I found the book wonderfully comprehensive in its analysis and explanation of deep ecology. The book delves nicely into the sources of deep ecology and its response to other perspectives on environmental issues. I found it a quick read (I read it at the gym, but then, I read Heidegger for fun) and well put together.
It will not, however, make someone who is coming from a perspective far from deep ecology change their mind. For that I would recommend Muir or Jeffers or better yet, spend some time in the real wilderness yourself. What it does is provide extensive background material and elucidation of the philosophy to someone who already believes in the importance of wilderness preservation.