Parks & Recreation defines its characters extremely well. Everyone has a role in the dynamic of the show, and while the nature of comedy & drama demands those roles be stretched and challenged from time to time, the show always knows what its characters are about.
The major exception to this rule is Ann Perkins. Ann started off as a plot device: She wanted the pit behind her house filled in. She volunteered to help Leslie get it done, and followed her through all the bureaucracy and crazy shenanigans that involved. Along the way she and Leslie bonded as friends, and Rashida Jones settled into the role of playing straight man to Amy Poehler’s insanity.