Its made by smallish groups of people and isn't focus-grouped to death.
As such its not always perfect and its full of little details to enjoy, like Joe Lycett deciding to 'steal' something in each task, Rhod Gilbert's solution to tying himself up, or Jason Mantzoukas... being Jason Mantzoukas.
It isn't that these things can't be pre-planned or written, it's that they're more enjoyable because the audience knows these came from the pressure of being given an unknown task.
It's genuine.
It's an absolute casserole.