i agree with Janzoon the first seasons are heavily focused on bart and overall the series is more story driven.
Later on the series they focused more on their characters mannerisms than the story.
i saw the whole series outta sequence but i would say around season 7 or so the series arrives at a different dynamic
The transition is very subtle so i can't pin point exactly when it happens but homer starts getting dumber and Lisa starts dropping witty and sarcastic comments and Bart starts being less rebellious and starts being more aware of himself.
I remember in one eps Bart is trying to win a girl's affection (i think it was the preacher's daughter) but she keeps ignoring him and he says:
"Why doesn't she like me? is it because ive been wearing the same clothes for 7 years?"
That joke always stuck with me for some reason.