A book I really wish had done better is my sci-fi erotica book, Shards.
Shards started out as a different take on the usual alien possession plot, instead having the alien being preserve the mind of the woman she possessed by moving her into her husband's brain, with the intention of eventually occupying their first baby and restoring the wife to her body -- so long as the wife can operate her husband's body to accomplish the deed!
It took a different turn when I decided that the alien came from a hermaphroditic species and wanted the baby to be one, too. It expanded from there into a virus spreading the same kind of genetic changes to all of humanity's future children and transformation of my characters into similar hermaphrodites. It was both challenging and fun trying to figure out what sex in their altered form would be like.
