I'm gonna put it in the most straight-forward manner possible: this thing is highly unparalleled when it comes to originality.
The concept is incredibly refreshing. Satan travels to Earth after being forcibly exiled from his original world... and ends up working as a part-timer to survive in a vastly different setting from what he was used to. High jinks and hilarity ensue for Satan and the people he meets along the way. There's action. There's comedy. There's even a cute, busty girl with a huge crush on Satan tossed in there just for the sake of it.
Suffice to say, this was a REALLY great show.