I think that the show just loses it's humor the longer it goes, at least there are a few jokes in the new ones. Maybe.
My favorite Family Guy quote would be when they're watching TV and there was some show showing bloopers and they had the character say "She sells seashells by the seashore."
Girl: Hey [guy's name...I forget it] what does your mom do for a living?
Guy who I forgot name of: Oh she sell seashells by the..
Bear breaks through side of house and mauls him
Peter: Yep, that's a tongue twister alright.
Or my favorite moment was just when Brain asked Lois about her feelings about her marriage and she said, "Eh, I just bottle those feelings up." Then it showed her brain and there was a lump on it going back and forth going, "I'm a tumor, I'm a tumor, I'm a tumor. I'm a tumor, I'm a tumor, I'm a tumor. Oh ah ah ah! I'm a tumor."