The characters have become terrible, insanely limited, very unrealistic and stupid.
Abed was a bit weird but not completely psychotic. It's done what almost EVERY comedy does, the characters become caricatures of themselves.
think Friends, they started as relatively rounded characters, Rachel was supposed to grow from a spoilt rich ***** to a normal adult. Which she probably did, Ross got more ridiculous but was still good, Joey went from stupid sometimes to ONLY being stupid. Monica went from sometimes a bit OCD to only the over the top part of her character. Pheobe went from a normal/whacky character to ONLY whacky.
The majority of shows can't help but take the biggest most different parts of the characters they start with and push towards those being the main part of the character and nothing else. This is what has absolutely happened with Community and it's exactly why Pierce, Britta, Abed, Shirley have become entirely boring. Abed isn't really weird sometimes in a funny way, he's just always weird now and it's not funny at all any more, not really. The nick cage thing would have been much funnier if he didn't do something similarly crazy and out there every episode. I saw it coming the second, the very second he said don't do a marathon, the entire scene coming was clear as day.
The show has done what the majority of shows do and turn complete characters into heavily limited, very narrowly focused characters who can always only react one way to everything. Characters growing into new COMPLETE characters that are multi faceted, great, almost no shows do this. Characters growing from the say 5 sided initial character, into a new but 1 dimensional character is not good writing, and it is what the majority of shows, particularly comedies/sitcoms, end up doing.
As said before, they set up the show in the first episode while being funny, there was no reason setting up how the show would play out in the new season couldn't be equally as funny and brilliant, it wasn't, that is an incredibly bad sign for me. They sacrificed comedy to tell a story, which just suggests they can't do that any more. The entire first season was telling a story in a damn funny way every week......