I dont really enjoy many long running american tv shows simply because i always loose interest and i hate waiting half a year only for it to end in a cliffhanger and go on for 10 seasons. Most of my favourites have been short lived ones. I love Firefly for example and if it had been 100's of episodes long like Stargate I doubt I would have bothered with it after I saw Serenity. I used to watch shows like 24 and Lost and just lost all interest and I rarely get stuck into the big, ongoing american series. The only one I have is with Chuck and im hoping it doesnt go on past a 5th series. I dont want to see it dragged out too much and i want to be able to go back years later and rewatch them all and when theyre 10 series long and beyond i can never be arsed with them anymore.
Anyway some of my favourite TV series which I will happily rewatch over and over include
Fawlty Towers
Chuck
The Day Today/ Brass Eye/ Knowing Me Knowing You/ Im Alan Partridge (Chris Morris and Steve Coogan are fantastic)
Flight of the Conchords
Spaced
Operation Good Guys
Firefly
Batman: The Animated Series
Family Guy
Almost all of them are comedies I guess. Its only the two animated ones that have a shitload of episodes.