The reasons for this very much comes down to the tone and content of the majority of the episodes. I guess in some ways you could argue that the audience that started watching the show three or four years ago, are not three or four years older so thus tastes and what they are used to is also older with them – however for me the show as it was worked for that age group already and the fourth season does feel like it would actively exclude younger viewers who may enjoy the previous seasons. Season 3 seemed more balanced in this regard, but the fourth season is the first that seems to have really clearly pushed for a much older audience in terms of older teens and adults.
I did not enjoy the second season of this show quite as much as I enjoyed the first, mainly because I felt the universal nature of it working for older children and adults had not been done as well.
