I feel like American Dad is where McFarlane is putting all his comedic potential because Family Guy seems to be running on autopilot. The first 3 seasons will always be classics, 3 being my personal favorite, but after a decent start to season 4 and a steady decline into more obvious humor I just couldn't get into it anymore. I dunno if it was the oversaturation of side characters the new writers dug up from the first 3 seasons (including overusing Herbert to the point where he lost his charm), the really, really long jokes you know had that "if it goes on for too long it'll surpass not being funny and become funny again" vibe about them, the change from semi-obscure movie/80s references that suddenly jumped to really obscure references that lose the joke on about 95% of the audience, the increased frequency/irrelevancy of the flashback sequences, or just the lack of wit in the jokes, which seasons 1-3 had. I find a lot of stuff funny but the only people these new episodes seemed to make laugh were my old stoner roommates.
Two other things:
The Cleveland show sounds like the result of McFarlane and a bunch of buddies drinking and laughing then one guy goes "dude....we should totally make a show about Cleveland!". Once everyone thinks that concept is so ridiculous it's funny they spout off dumb ideas that are equally as ridiculous which makes them funny in a very sad, stupid way. Then these ideas turn into a show. At least that's how I envision it from the concept because I don't care how confident you are, making a spin-off based on the most boring character in a show is incredibly stupid.
Another thing, the giant chicken fights were never funny. Ever. The first one had charm because of its randomness but when they brought it back it was clearly the new writers lacking any good material and reaching back to take anything they could get their hands on.