The first book was really interesting. Everything was written close to historical as possible (at the time, though what we know has changed since then), with the exception of the main character being given credit for every huge leap of inspiration (fire, domesticating animals, understanding reproduction...)
I skim through large sections of descriptions of the lay of the land, and through (at least in every book past the first) frequent caveman sex scenes, but the dialogue, and interaction in the different cultures is fascinating. It is definitely worth all the boring parts.
5 year old girl sees her family get swallowed up in an earthquake, she travels on her own for days with nothing to eat, and collapses, is picked up by a tribe of neanderthals, and raised by them. She doesn't quite fit into their society, but does her best, eventually being tossed out and having to go out on her own to search for her own people. In the process, she gets passed around from culture to culture, amazing everyone she comes across, and teaching them things she has learned.