[Apologies to my British readers who already know this. Back me up in the comments.]
Of the not insignificant amount of television I was exposed to in my two years living in England, Green Wing was surely the best of the bunch. It is an hour long comedy with an ensemble cast centered around a hospital. There is is a story in the sense that things happen, but there is not really a "plot" to the episodes: each episode shows a day at the hospital and maybe the aftermath at a bar or something.
Comedy relies on surprise, and Green Wing does what Adult Swim did when it first premiered -- jokes always come out of left field. This is harder to do in live action than cartoons, where there is more range for the anarchic -- but Green Wing pulls it off. Part of the genius of the show is that underneath all the madness is a hospital drama about a new female doctor trying settle her romantic feelings for two of her colleagues. I think that plot only serves to lull us into a false sense of security at regular intervals, before ABSURD jokes like I have never seen come flying out of nowhere. Hour after hour the show continues to surprise, which is not an easy thing to do.
When something dull is going on the film speeds past it and when something interesting is going on the film slows down to catch it. The editing, on one level, is not exactly rocket surgery, but coupled with an amazing, original, and indispensable soundtrack the show taps directly into the idea that comedy requires perfect timing and rhythm to work. This principle is usually reserved for describing single jokes, but Green Wing essentially replaces story structure with a comic rhythmic structure on a much larger scale.
I could go on about the show for days -- including Dr. Alan Statham who is surely one of the great comedy creations (though his first scene is not representative of the genius of the character). But someone put the first eight and a half minutes of the first episode up you YouTube, so here it is for you to see for yourself -- much better than me trying to put examples into words.
[As a side-note I often hear people wishing they would make Region 1 DVDs of British television. Do what I do -- get a region free DVD player (not even that expensive) and then get DVDs through EBay or whatever. British TV rocks.]