I think most of the original run is still good to this day, minus maybe a few stinkers I've forgotten that every show has.

Everything from that moment on has been trash, and the only times it wasn't trash was when it was deliberately trying to manipulate you like the episode with his Mom trying to ape the Dog episode.

I still can't decide of the Evolution episode, the Gay marriage one or the not-Obama one is the most actually offensive thing I've seen a show try to pull. Not throwaway jokes like Family Guy or South Park, but full on no subtlety liberal propaganda spots.