How bad is it? It's one of the worst barbarian crossed with sci-fi films (yes, there is more than one of those).
Should you see it? It falls apart, but watch the first half and see how it goes from there.
A blonde among brunettes seeks his own kind (sort of a male Clan of the Cave Bear), with a medallion around his neck to guide him. This caveman fights Neanderthals in an entertaining first half, but then discovers a post-nuclear control center run by an overlord. From there, it's robots, ray-guns and nuclear weapons and the caveman thing doesn't really work any more. There's dinosaurs, blue-faced ape men, fire worship, hang gliding from a pterodactyl, cavewomen in leather skirts and boots.