As wonderful and funny and entertaining as the first season is, the way that the characters never seem to grow or change much despite going through these massive internal struggles and winning the day by having their moment of great insight, they then pointlessly repeat the cycle with a less interesting villain in the next series and the series after that.
The show, just like the characters never really evolves, it just repeats itself conceptually over and over, a massive shame since the first season was so great, and the following seasons have lots of great ideas and well written dialogue and performances, despite all that I find myself skipping through the later episodes because of their predictability.
If I was only rating the first season I would give it a 9/10, but as each season after the first gets worse I sort of gave the show an average rating.