I don't just throw this about willy-nilly. I had my prologue read by a companion, and she said she was so disgusted by the villain that she almost stopped reading. And she wasn't referring to the captain of the pirate ship, who is the true villain of the piece. No, it was the MC's fiance, who was 10 years her senior. The current prologue of Griffin's Song is written from the fiance's point of view, and how he decides he wants to marry Sarah. He is 20 at the time, and she 10. Apparently it was disturbing. What if other people stopped reading then?
It happened to me once or twice. The first time was when I read Second Ship by Richard Phillips. There was such a graphic scene of violence, and psychological terror that I had to put it down for a year. I finally pushed through it, but only because it had hurt my pride that I hadn't finished. Then it happened again later, with Brisingr by Christopher Paolini. The opening chapter concerns a viewing of self-mutilation in the form of cutting off limbs in offering to horrible creatures. I couldn't read further. Later I did, but it was a close thing.
So I put this question out there: can a villain be too well done?