Since Gurps Ice Age is from 1989, it's obviously a little dated. (Tyrannosaurus rex is a carnosaur? What's the Tertiary?) But it's not too bad. It's missing a few of the more recently discovered hominids, like Homo floresiensis ("hobbits"), but covers the core taxa (Australopithecus, H. habilis, H. erectus, ancient H. sapiens, Neanderthals, and Cro-Magnons). The discussion of their technologies, language, and the development of culture and particularly religion is pretty good, albeit brief. The overview of the Pliocene isn't bad, but seem a little too short even for such a thin book.

The game parts seem decent, though a -2 penalty to IQ and a language skill cap doesn't seem sufficient to account for the vast different in intellect between H. erectus and modern humans, and the same applies to the other early humans. The section on shamanism seems functional, though it predates GURPS Voodoo, so Ice Age magic is unfortunately based on GURPS Fantasy-style magic instead of using rituals and paths. They also missed an opportunity -- the book talks about how even if magic is not real, the early human belief in it would still lead to real effects, but they never translates that into anything concrete. So either you use spell points, or magic is just flavor. The bestiary is okay, though the stats don't seem very rigorous.

The section on campaigns is short but excellent, covering the key campaign styles and themes, from fleeing a disaster to slapstick. Pointing out the two periods in prehistory when multiple species/sub-species of humans co-existed is very useful. The concluding adventure "Wolf Pack on Bear River" is pretty good.