Low 4/high 3.
In contrast to Brian Fagan’s Human Prehistory and the First Civilizations this is considerably more focused. It’s also a more recent creation and, in the rapidly advancing field of human evolution and archaeology, this is critical.
My one big complaint about this is that it’s not very well organized. Stringer seems unable to keep focused, instead he constantly make references to things he’ll cover in other chapters. This is NOT an issue with the subject matter, as Jared Diamond avoided this problem handsomely in his excellent (but slightly dated now) The Third Chimpanzee: The Evolution & Future of the Human Animal.
In general, the technical level is on the high side, so I wouldn’t recommend this to someone just getting into the subject. But, if you have some familiarity with the field and can tolerate the poor organization, it’s worth a read.