To me the seasons 1-3 of That Mitchell and Webb Look offered the best sketch comedy in recent years. The show managed to be laughably funny in a traditional way, yet innovative and modern. Season 4, the last to date, is very different. It still has plenty of sci-fi, fantasy and historical themes, but the overall tone is even more surreal in a slightly darker way. It is also much less funny.
Dark, surrealist tones in comedy are often associated with high intelligence. This isn't always true. In fact the earlier seasons of Mitchell and Webb Look (& Situation) were more light hearted AND appeared more intelligent. The combination of darker tones and fewer fresh ideas gives all the six episodes a tired and depressed feel. At times the episodes even feel difficult to sit through. However, both Mitchell and Webb are still good comedians and there are some laughs, so one star material this is not.