Well, I consider 2 seasons (TSCC) a fair chance. And as I said recently in the Dexter review, I actually prefer shorter runs or even a cancellation over shows that go on and on. For network shows, that is even more true. Who really needs 9(?) seasons of X Files. Or 7+ seasons of 24.
Then there is Firefly. Yes Fox, misthreated the show. But what we have in the end is a short and mostly brilliant run that ends on an artistic high note. To me, the movie Serenity was already a let-down, comparatively. Who knows how much Firefly S4 would have sucked, with Marti Noxon taking over and Joss Whedon working on Dollhouse.