Game of Thrones gave viewers Daenerys Targaryen to root for. She started out as a mere abuse victim and eventually became one of the deadliest forces on the show. For many seasons it appeared that she would end up being a hero so it was unsurprising that many were taken aback when it was revealed she was the ultimate villain on the show.
Well there had been clues sprinkled throughout the show that it was possible for Daenerys to become evil. Just you had to have been looking for those clues as the show preferred to completely hide the twist instead of rewarding observant viewers.
Animorphs did the opposite with Rachel. The book series fully acknowledged that she was wavering between succumbing to her bloodlust and staying true to her humanity. So when she made her choice it made absolute sense.
