The Shelters of Stone by Jean M. Auel
Over a decade ago, I read the famous Clan of the Cave Bear and liked it, though I never read the sequels. So when, a couple years ago, I started hearing of the vitriol Auel got on all her sequels, especially her latest The Shelters of Stone, I got more and more curious.
After reading This post on "good plot, bad author" day here, and This hilarious MST of one of Auel's sex scenes I couldn't restrain my curiously any longer.
It was indeed pretty bad, but not in the way I'd thought it would be.
Review here.