Two examples: Arrested Development - truly brilliant, very cleverly funny and very well written, only 3 seasons.
Pushing Daisies - Hilarious, yet in a weird morbid kind of way with a unique structure and genius concept. Only two seasons (though it was technically one season split in two cos of the writers strike...)
Yet some of the really crappy generic sitcoms get many seasons under their belt!
@Sir Thursday - Completely agree, The only bright spots in season 4 were the arrival of Lois Lane *drool* and the episode with the Flash - he is my favourite superhero.
