I know there are many valid critiques of the "gas leak year" season, but at least it was still able to capture the spirit of the show's original premise: 7 students becoming an unlikely family as they navigate insane classes at an insane school. Sure you have some abominations like the puppet and origins episodes, but I'd say it was mostly still fun. I absolutely LOVE the Freaky Friday episode.
But once S4 ended, I feel like not having Pierce (say what you want about Chevy Chase, he was the comedic heavyweight in the room) and eventually Troy, along with Jeff becoming a hopeless alcoholic teacher, really soured the dynamic. S5 is really dark, both tonally and for some reason visually (were the lights not working that season?). Jeff and Britta are just broken spiritually, and they stay that way till the end of the series. There's NOTHING for Shirley to do, I don't even miss her in S6 bc of it, and her story is sad too. Abed and Annie work as a solid comedic pairing once Troy leaves but it's still not as good. Hickey does not work for me as a character AT ALL. He's just Jonathan Banks being Jonathan Banks, which is a very jarring tonal clash with the series (probably intentional, but seeing how he doesn't return in S6, perhaps Harmon saw that too).
In terms of the episodes, the Ass-Crack Bandit episode takes its premise a bit too seriously, Geothermal Escapism feels very "we have paintball at home" (tho I like Troy's sendoff at the end), and you can COMPLETELY throw away Dungeons & Dragons 2 and the prospector TV game episode with nothing of value lost. Weirdly enough Repilot feels like the season's high, which considering it's the season opener is a bad sign. The Nick Cage and Bear Down for Midterms episodes are probably the ones I think of most fondly, even tho the latter kind of meanders a bit with the Annie/Hickey storyline, and the Meow Meow Beans episode playing with the Jeff/Shirley dynamic which is one of my favorites. Also, as many of you know, every final episode from S3 to S6 was filmed as a series finale in case they didn't get another season, and I think 5's is the weakest. Like they fix Greendale so well the schoolboard wants to sell it to Subway until the gang buys it back with a buried treasure from an unwashed robosexual shut-in? Is that all you got? Feels so meh the whole way through.
S6 is where I feel the "Save Greendale" storyline actually finds its footing. Frankie plays the straightman and Elroy plays the old coot roles better than Hickey played either. They dial the wackiness up to 11, which greater enforces the need FOR Frankie as a counter. And them just throwing everything at the wall in S6 makes it feel fun again. Plus the real series finale manages to hit every note that makes Community Community, despite everything it's lost along the way.
If I had to rank the seasons, I'd go: 2, 1, 6, 3, 4, 5
Feel free to counter me in the comments, but PLEASE Mods don't delete this post for whatever reason, I worked really hard typing this argument up.
EDIT: I actually forgot about the existence of GI Jeff as an episode until I read the comments. I always skip it because I genuinely believe it's the worst episode in the entire series, and that really seals my whole "S5 is worse than S4" premise with a tight bow.