Snape was way too poised and sympathetic in the movies, if the tv series were to be faithful, they first should find an actor that matches the description of Snape. Alan Rickman is much older than book Snape and way too good-looking and elegant, we can chalk that up to older Snape has matured and is much more stoic, but HBO focusing on the age and not the literally physical description of Snape, while simutaneous making him more sympathetic is way out of touch with the source material. For the majority of the book, Snape was an absolute menace and a wreck, which is what makes his ultimate sacrifice so shocking. He was clearly picked on for his appearance as well, Papa is a terrible casting choice.