I can't say I agree with Moviebob on this one. His views and analysis are certainly interesting, but his hypothesis that the original Simpsons episodes worked so well mostly because they were a parody of stereotypical American TV storylines is, well, a bit America-centric, really. I'm British, and I never grew up with that kind of influence (except for Friends. God I loved Friends), yet I loved The Simpsons, not because it was slyly pointing out the humour in the American pop culture of the period, but simply because I thought it was funny. Well, to be fair, I was pretty young, and seeing a man fall repeatedly down a large gorge is the kind of thing that can reduce any child to hysterical laughter.
Personally, I feel that it just got too familiar, and familiarity breeds contempt, or at least boredom, which can be equally fatal. A lot of the earlier episodes focused a lot on the family and their interactions with the world around them, but you can only explore a character so much before you've more or less explored everything, especially when they're trapped in some sort of eternal time-lock, trapped at the same age while the world around them moves on. Homer can only mess up so many times, Bart can only play a finite number of pranks, Lisa face a new issue of social awkwardness or rejection, and ventually it's going to start to get stale. This, I suggest, is why a lot of the newer episodes became simple flat-out satire (pick a popular thing, then mock that thing for the entire episode, and repeat until the season is done), because the characters themselves had been fleshed out as much as possible. The sad thing is, everything, even TV shows, have to die.
Personally, I feel that it just got too familiar, and familiarity breeds contempt, or at least boredom, which can be equally fatal. A lot of the earlier episodes focused a lot on the family and their interactions with the world around them, but you can only explore a character so much before you've more or less explored everything, especially when they're trapped in some sort of eternal time-lock, trapped at the same age while the world around them moves on. Homer can only mess up so many times, Bart can only play a finite number of pranks, Lisa face a new issue of social awkwardness or rejection, and ventually it's going to start to get stale. This, I suggest, is why a lot of the newer episodes became simple flat-out satire (pick a popular thing, then mock that thing for the entire episode, and repeat until the season is done), because the characters themselves had been fleshed out as much as possible. The sad thing is, everything, even TV shows, have to die.