I'm a computer scientist with background in theoretical discrete math rather than experimental sciences ("Concrete Mathematics" is I think my favourite math book). This is probably why I'm a bit put off by "loose" treatment of mathematics by some students of "applied" subjects: "all functions are continuous", "all sequences converge", and so on. Not in this book! Although the author puts strong emphasis on concrete, practical examples, his reasoning is clear and precice. You just feel that he's honest with the reader; if the proof of a theorem is beyond the scope of the book, he clearly says so without pretending that he proved something he didn't.

But don't think that the book is full of precise, but boring, formal derivations. Exactly the oposite, the exposition is mostly informal, getting rigorous exactly when it's necessary. Material is presented in the natural way, starting from simple questions and simple examples, towards more general and complicated things (just as in "Concrete Mathematics"). On the one hand, none of the "let's start with some definitions" statements where for the first 200 pages you're wondering about the purpose of the theory. On the other hand, none of the "to solve problem A we apply method B" statements which explain "how" but not "why".

And probably the most valuable thing in this book are diagrams. You can almost read the book without reading the text, just by looking at the diagrams. You can hardly find a page without one or two of them. From my experience, preparings good diagrams requires a lot of effort, and I'm very thankful to the author for making them. They are crucial to enjoy the book.