While season 4 wasn't as strong as its predecessors, it still held up. Season 3 got pretty gimmicky in places -- in case you pushed the anime scene from the foosball episode out of your mind, I'm here to remind you it happened -- though I'll admit season 3's strongest episodes were better than anything we saw in season 4.
Season 4 wrote Shirley very well, though, and I'm glad for that. Seasons 1 through 3 pretty much had her as a foil for the rest of the group.
Season 4 is barely funny at its high points, and there are few of them. It may compare well to the average tv comedy, but compared to Seasons 1-3, it's shit on a shingle.
I hope more content creators can offer their stuff on amazon or netflix directly instead of relying on mainstream tv networks. Maybe they'd fare better by microcasting and not having to worry about timeslots and nielsen ratings.
A big part of Community's popularity were the theme episodes, which are ridiculously expensive. Like it or not you couldn't make the paintball episode or the zombie halloween party (with ABBA soundtrack!) without a network budget, and it's no coincidence that as every season's budget gets smaller the show gets less funny.
I'm not going to argue that point, but almost every time I like a show it's like the thing has the kiss of death. I'd like to see them have more of a fighting chance.