As a teacher and an Evolutionary Biologist, it's disappointing that there aren't many textbooks or scholarly works, particularly in the field of evolution, that are both accessible and scientifically rigorous. Doug Futuyma has done an excellent job of making this work both.
Textbooks are unfortunately often written by professionals who seem more interested in impressing their colleagues with the elegance of their explanations than in presenting their material in an easy-to-understand way for students. What we teachers usually end up with in those cases are texts that make our job more difficult, forcing us to re-explain material that students have already paid lots of money to read. This book does a good job of keeping that to a minimum.
This is not an easy task with a subject like evolution. First, evolution is not simply "survival of the fittest". In fact, it's hardly that at all. It is vastly more complex; it is a very elegant process by which much of the complexity of our universe, particularly living systems, came to be.
Second, evolution has been so misunderstood, and misrepresented, both intentionally and unintentionally, for so long, that it is often difficult for the uninitiated to understand what biologists really mean when we talk about it. This is becoming even more of a problem as other fields of study, particularly the Social Sciences, see it's utility and begin using it without always understanding it completely. The result of all this is that the common view of evolution bears little, if any, resemblance to the scientific theory.
I used an earlier edition of this book in my first undergraduate class in the subject, and today as a professional Evolutionary Biologist I still keep it on the shelf over my desk as a reference and teaching aid. I recommend this book to anyone who seriously wants to understand evolution and why all modern biology is built upon this single theory.