I think The Thick Of It outstayed its welcome. Chris Langham, notwithstanding his personal life, was superb in the first series. I liked the specials and the third series, but the fourth was when the wheels truly came off. The coalition and the Tories were not as funny and each episode seemed to deteriorate into just a lot of shouting. There were a couple of good episodes, like the ousting of Rebecca Front's character and the inquiry episode, but it did seem like it was seriously running out of steam in the fourth.
Red Dwarf is perhaps the best example. Series 7 onwards it really fell apart. Red Dwarf was a unique sitcom; clever, with dark dystopian sci-fi themes and original ideas from which the comedy emerged organically. It seems that Rob Grant was chiefy responsible for the sci-fi and story elements and Doug Naylor was the gag-man because after Grant left, it just became like any other sitcom. A real shame.
You haven't met the Groper yet have you................you will when he's read this post. 
