American Dad is a show by Seth McFarlane, who is also well-known for creating Family Guy. Unlike the latter, American Dad is a well-written, satirical comedy for politically conscience people. If you don't have a certain degree of intelligence, it's unlikely you'll really grasp the humor used in the show.
Family Guy fan-boys are notorious for bashing American Dad due it being non-repetitive.
Although one may not like the show, it's hilarity can't be denied.
Family Guy fan: "DUDE! American Dad is SO lame!"
American Dad fan: "Go crawl back under your rock fan-boy!"