I'll put some from Seasons 1-3:
S1
Overrated: Ripped Pants, Boating School, Fools in April, I Was a Teenage Gary
Underrated: Jellyfishing
S2
Overrated: Something Smells, Wormy, the 27 duo (Prehibernation Week, Life of Crime), I'm With Stupid, The Fry Cook Games
Underrated: Dumped, Squirrel Jokes, Pressure, Krusty Love, Squid On Strike
S3
Overrated: SpongeGuard on Duty, Nasty Patty (very overrated), MMBB4, Doing Time, Squilliam Returns (very overrated), Chocolate with Nuts (this is just good, not anything special), New Student Starfish, Clams (very overrated), Born Again Krabs, SpongeBob Meets the Strangler (very overrated)
Underrated: The Bully, The Sponge Who Could Fly
S1
Overrated: Ripped Pants, Boating School, Fools in April, I Was a Teenage Gary
Underrated: Jellyfishing
S2
Overrated: Something Smells, Wormy, the 27 duo (Prehibernation Week, Life of Crime), I'm With Stupid, The Fry Cook Games
Underrated: Dumped, Squirrel Jokes, Pressure, Krusty Love, Squid On Strike
S3
Overrated: SpongeGuard on Duty, Nasty Patty (very overrated), MMBB4, Doing Time, Squilliam Returns (very overrated), Chocolate with Nuts (this is just good, not anything special), New Student Starfish, Clams (very overrated), Born Again Krabs, SpongeBob Meets the Strangler (very overrated)
Underrated: The Bully, The Sponge Who Could Fly