The two poorly-rated “classic” Simpsons episodes are both clip shows (the second and third such episodes):
S06 E03: Another Simpsons Clip Show
S09 E11: All Singing, All Dancing
The first clip show episode, S04 E18, is lower-rated than its neighbors but still gets a 7.0, perhaps because of the IMO hilarious “April Fools” framing narrative.
Also notably unpopular classic episodes:
S08 E24: The Simpsons Spin-Off Showcase (three non-canonical segments that are deliberately bad for the sake of humor)
S09 E02: The Principal and the Pauper (Principal Skinner is revealed to be a fraud)
The two poorly-rated “classic” Simpsons episodes are both clip shows (the second and third such episodes):
S06 E03: Another Simpsons Clip Show
S09 E11: All Singing, All Dancing
The first clip show episode, S04 E18, is lower-rated than its neighbors but still gets a 7.0, perhaps because of the IMO hilarious “April Fools” framing narrative.
Also notably unpopular classic episodes:
S08 E24: The Simpsons Spin-Off Showcase (three non-canonical segments that are deliberately bad for the sake of humor)
S09 E02: The Principal and the Pauper (Principal Skinner is revealed to be a fraud)
I always liked the spin-off showcase
I give All Singing, All Dancing a pass solely for the “Paint Your Wagon” gag.