Putting the classic elements of a good comedy together does not necessarily make a sitcom successful. This episode has a plot based on the Crane brothers' snobbery, which is not that original, with their repeated thwarted attempts at getting theatre tickets becoming irritating after a while. The secondary characters are wasted and you get the idea that some elements are a bit too familiar. The Cranes trying to meet some famous artist? Done. The Cranes and a famous (British) actor? Done.
A few one-liners and the excellent acting of everyone involved (although Fritz Weaver's accent is a bit wobbly) save it slightly.