As an Intro Psych instructor, I reviewed dozens of psychology texts. Gray's "Psychology" is clearly the best.
First, because it is written by a single author, it maintains a consistent style and viewpoint throughout--that is, the application of evolutionary biology and cognitive science to the study of the mind and behavior. Consequently, he does not shy away from putting forward strong arguments where they are needed. On this, see especially his superb discussion of the fall of behaviorism and the rise of cognitivism.
Second, the author has a powerful command of several lines of important research, and he uses this to "smarten up" the text to make it *more* understandable. As an example, see particularly his discussions of the heritability of intelligence.
Third, the text is beautifully organized.
The text does, however, suffer from two small weaknesses: the discussion of self-esteem owes too much to James, with James' errors especially, and the discussion of mental health and happiness needlessly bore little imprint from the chapters on cognition.
Still, Gray produced a superlative volume.