No, actually, Family Guy is not funny. It's cheap. It's for idiots.
What MacFarlaine does is takes a TV show or film and makes fun of it with a deliberate, almost flagrant knock off of The Simpsons. He always shoots for something low-brow, knowing precisely who his audience is. He has no use for anything remotely decent.
Contrast that with Cheers or Frasier, something far more intelligent. Or how about the Marx Brothers? Seth is a mental dwarf compared to those talents.