Short version: terrible.
Medium version: think 300. This movie is very similar to it in terms of both connection to reality and the overall flow.
Long version (WARNING: a plot spoiler): there's this really advanced civilization in the middle of desert 12000 years ago. They know metalworks (and it looks like iron, too), shipbuilding, navigation, astronomy, writing, cloth manufacture. Basically, Atlantis, except in Africa. They build huge gold-tipped pyramids, elevated roads, and babylonian-looking temples and are rulled by a priest class reporting to chief priest AKA the "Almighty". To build all this they need, obviously, slaves, and so they send the roaming bands to snatch them from neighboring tribes.
The neighbors are more authentically looking 10000BC-ers (at least they wear fur, and appear to not use iron weapons). The only problem - their men are either shaved, or have neatly trimmed beards and goatees.
Anyways, one of these roving bands steals this good-looking girl, and it proves to be their undoing: her boyfriend comes to rescue her, incites the global slave revolt, easily overcomes the few armed (iron swords!) guards that are there. In the thick of the fight the gilfriend gets shot, but then is magically revived by a magician thousands of miles away.
Oh, yes, and at the end of all this our hero's tribe gets a bag of magic beans and starts the agricultural revolution. Viva Monsanto!