As I have now seen the series several times I decided to rate the episodes to the best of my abilities. I can explain any particular ratings if anyone wishes and I would be interested to see if people here agree/disagree with them.
MY RATING SYSTEM:
10/10 - perfect (very rare)
9.5 or 9 - amazing (close to perfect)
8.5 - really good
8 - good
7.5 or 7 - decent but room for improvement
6.5 or 6 - average
5.5 or 5 - meh
4.5 to 3 - bad
2 or lower: horrible (very rare for this series)
NOTE: I am going by production codes available on nickandmore.com rather than common DVD and streaming listings for which episodes are in each season.
When Pants Attack - 8.5/10
Normal Boy - 8/10
Birth of a Salesman - 9/10
Brobot - 5.5/10
The Big Pinch - 6.5/10
Granny Baby - 7/10
Time Is Money - 8/10
Raise the Oozy Scab - 8/10
I Dream of Jimmy - 6/10
Jimmy on Ice - 6.5/10
Battle of the Bands - 8.5/10
Trading Faces - 7.5/10
See Jimmy Run - 3/10
Phantom of Retroland - 7.5/10
My Son the Hamster - 6/10
Hall Monster - 9.5/10
Hypno Birthday to You - 7.5/10
Krunch Time - 6/10
Substitute Creature - 6.5/10
Crime Sheen Investigation - 9.5/10
Safety First - 9/10
Journey to the Center of Carl - 8/10
Aughh! Wilderness - 9/10
Party at Neutron's - 9/10
Ultra-Sheen - 8/10
Broadcast Blues - 10/10
Professor Calamitous I Presume - 7/10
Eggpire Strikes Back - 10/10
Maximum Hugh - 6.5/10
Sleepless in Retroville - 6.5/10
Make Room for Daddy-O - 9.5/10
Love Potion - 10/10
Holly Jolly Jimmy - 5/10
Overall this season isn't as strong as seasons 2 or 3, especially in the first half. It started off with several mediocre or forgettable episodes ("Brobot", "The Big Pinch", "Granny Baby" and "I Dream of Jimmy" for example) which may have been because they were relying on freelance writers or still finding the tone for the series. Around 11 episodes in, though, it gets really good, with three of the perfect episodes ("Love Potion", "Broadcast Blues" and "Eggpire Strikes Back") coming up. The former is one of the best because it's the first one to really take the romance aspect of the show seriously, not to mention the hilarious subplot with Carl and Judy. Broadcast is really good because it's really funny, almost like SpongeBob's "Tentacle-Vision" done right. Eggpire genuinely feels like the movie. Except better. Overall I think several characters are underdeveloped at this point; Sheen is still mainly driven by his Ultra-Lord obsession, and Cindy feels more like an annoying popular girl as opposed to the angsty, Helga-like character she would become as the series progressed. "See Jimmy Run" is my least favorite from this season because of it's horrible portrayal of Jimmy and incredibly stupid ending. Most other episodes from this season with low points are just because I find them boring or dumb. I already explained why I don't like "Holly Jolly Jimmy" on that episode's discussion page.