Some of the jokes in family guy are funny. But you can only watch so many episodes before you notice the lack of structure and story to them.
I think the whole point of FG is to NOT have structure. They have a storyline or plot just because it makes sense to have one, and because it would probably be pretty hard to shop a "stand up cartoon comedy" to any networks.
Family Guy, I got into the show about a year ago. A junkie roommate of mine used to watch it, and I never thought I wanted to see the show due to the title. I happened to be in her room one night while the show was playing and heard about 5min of jokes, and was just laughing hilariously. I kept saying "I can't believe they'd go there and say that...and the networks let them?!"
Anyway, I think the writers know exactly what they're doing, and are all about pushing the envelope. They just want to be able to say things on TV that nearly every person thinks, but does not say for one reason or another. And being a cartoon, they can take that to another level without as many negative ramifications as being said by live actors.