It's success was more around its character development and the setting. It set up a lot of things that looked like they'd be used later, but while there were seasons left, people actually gobbled it up. Then the author/writers realized they wouldn't be able to tie up all the loose ends they left, and definitely not in two seasons, so it was unsatisfying. It also meant they were tying up loose ends and not spending time on the character development that made the show.