I think the problem is somewhere allong the line they decided to make Bart and Lisa centered episodes kid friendly. And while it doesn't talk down to them, sometimes it just directly talks to them. And if Lisa's social issues continue to be a theme, rather than the brunt of satire, they just get naggy and don't help but hinder the cause. Case in point, the one where Bart gets a cow... terrible episode (though I did like the line "For once in my line, I finally had a cow, Man!"), and not full of anything I already know.
Plus, the insistence of reusing the same characters that are a catchphrase at best. I'm sick to death of Cletus. He appears in every lousy episode. Yeah, he's a hick... we get it. And Sideshow Mel just coming up and saying stuff that ammounts to "I have a thick Brrrritish accent and rrrrrroll my Rrrr's! Isn't that hillarity?" I have no problem with stuff like that, but they use it way too much as cheap laughs. Even when they used to have Dr. Nick and stuff like that, the characters served a purpose.
The one thing I think Family Guy has over the Simpsons is that they have actually killed off a majority of those kind of characters... Paddy Tanenger... The Vaudeville guys... both had gruesome on screen deaths. And even Herbert hasn't appeared since Chris said to him straight faced "Are you a pedophile?" (I agree with that decision. They're no way to follow that one up)
And lastly, I hate how they made Marge too house wifey and talk similar to Flanders. I see they've decided to cut back on that (especially her line at the end of the movie "Just toss the GD Bomb already"). plus, so far this season seems to be alright.
I just hope we have no more extended flashbacks or views of the future.... those are the worst. They haven't had a decent flash back since the 90's... and speaking of which, "That 90's Show" (an episode last year about Marge's secret year of college) was pretty terrible, screwed up it's consistency... but Weird Al was in it, so it wasn't all bad.