the Clan of the Cave Bear is a great novel for completely different reasons, and not so ahistorical as you might think when it comes to recent Neanderthal research (I've been reading some popular paleoanthropology). It's completely fictionalised, of course - the neurological differences and culture are (by necessity) pure speculation - but not completely out of whack with the archaeological evidence. The Neanderthals really did have a remarkable stasis in their technology, as compared to anatomically modern humans. They did eat a lot fewer vegetables or small mammals and fish/seafood than is depicted in the book.