Family Guy was one of the first shows I watched on the regular. It premiered the year after I was born, and my dad was a big fan of it, so we had DVDs of every pre-cancellation episode. I watched them religiously and loved every second of them. When the show came back, me and my family watched it every Sunday night (9:00 on Global). Things were good, and the show was still funny.
Then the later seasons came. If I had to pinpoint an episode when it started to go downhill, it would be the first time they used one of those stock Conway Twitty clips. Even as a kid I knew it was obvious filler. As the show went on and on, every character became a simple parody of themselves (Brian now bares absolutely no resemblance to his pre-cancellation self) and the episodes became preachy liberal soapboxes. Now every episode has to end with a moral about being kind to one another or some nonsense, and it's just embarrassing to see the writing team try.
The show hit rock bottom with Season 13. Now the only jokes they make are about cell phone apps and the liberal smugness is through the roof. I don't want it regularly anymore, but I have to admit to torrenting all the episodes of the new seasons once they're over. I know the show is creatively dead, but I consider keeping up with it an obligation.