Buffy and GOT yes. Once doesn't belong anywhere near this list, fun but not quality at all. Samurai Jack doesn't fit in this category. Avatar is one of the best shows ever but again not really fitting in this category.

Supernatural and Battlestar Gallactica should be on this list, if we are talking easily accessible scifi/fantasy with modern storytelling .

X-Files is a classic sci fi show but I wouldn't call it accessible to the general public.