Instapundit quotes the Daily Caller headline, which isn't supported by what the actor Christopher Abbott ("Charlie") actually said or supposedly said. The actor's spokesperson said "he’s working on numerous other projects" and "a source" said "Chris is at odds with Lena [Dunham]" and "He didn’t like the direction things are going in." That doesn't mean he thinks the show is terrible. At most he's arguing with Dunham or doesn't like what she's doing with his character. My guess is: He's negotiating his salary.
Note: The show is not terrible. It's just — as sitcoms go — a grim picture. People are young and they get naked and have sex on occasion, and yet it's not fun. It tends to be dismal and dark. You'd think conservatives would know how to take that. Are they dumb or just unwilling to watch the show they berate?