The first three seasons are the best, no contest. The creators cared, the writers cared. They tried to make a family sitcom, plain and simple. No shock value, no grotesque imagery, no meta humor, no political pandering. Nada. The fourth and fifth season, while taking a sharp change in quality (as a result of the uncancellation), it did have, dare I say, humor and wit.
However, from the sixth season then on, the writing (or lack thereof) is consistently poor and simply bad. The jokes are desperate, they aren't funny. All the characters got flanderized to the point they fit a single descriptive word; they are that one-dimensional.
In recent seasons the writers have been trying to catch a sense of progression and character development but it just doesn't work. The damage has been done. It's even worse because the writers don't do it well anyway. As another has said before, there's also a lot of odd and pointless oddball characters and significant plot and character set-in-stone details and retconning.
- Peter having a secret sister, despite all previous seasons suggesting he is the lone biological child of his parents.
- Peter's name being "Justin" on his birth certificate, again never mentioned, only for one episode, all jokes related to the matter aren't funny and his name is legally changed to Peter in the end, rending the whole episode pointless.
- Quagmire having a sister when never mentioned in any other episode but the one, and it was for an awful political campaign, she never reappeared again.
- Meg finally arguing with her family, upsetting them, yet in the end she is suddenly not the victim, accepts to be the family's punching bag, and acts happy about it. (Episode: Seahorse Seashell Party). Upsetting many long-time viewers.
- Many characters getting killed off (Muriel) for no reason, other characters (Neal) from previous seasons having little to no showtime, reducing and retconning many aspects set by the earlier seasons.
Among numerous others I can't remember. It's just a mess of a show. It should just be cancelled at this point since it's obvious the writers don't give a damn in the slightest to have a sense of common decency and quality for their own product and the production company and FOX for eating it up for ratings and money.
Personally, if I want some dry and cheerful humor, I watch Bob's Burgers. Otherwise, American Dad still has me cracking up now and again.
