Yeah, McFarlane shows aren't meant to be deep in any way. And I agree about his politics -- though ironically, American Dad remedies a lot of that. Whenever there's political humor in American Dad, it's oddly nonpartisan. Since Stan Smith is basically the ULTRA SUPER MEGA REPUBLICAN and his daughter Haley is basically the ULTRA SUPER MEGA DEMOCRAT, they're both pretty much constantly spewing the most over-the-top, unrealistic political rhetoric you can imagine, and it balances out quite nicely into the realm of "no specific political agenda, just making fun of politics in general."
When it comes to thought-provoking American cartoons, the best are probably Futurama (where's the new season of that, anyway?) and, oddly, South Park. South Park is blunt as a hammer, but its humor is soooo timely and clever, and really does an incredible job of satirizing modern American society.
-Tom