I've noticed in recent years that good well written tv. shows only last roughly four seasons. BSG comes to mind first as well as Enterprise, which one could argue was poorly written. Now we have Breaking Bad and a few other good shows are ending after their fourth seasons. Obviously a few factors come into play these days, production cost, actually paying writers, reality shows, too many chanels, and many other problems. So it seems like all of these factors plus the attention span of Americans continues to dwindle. So we end up with most channels having one or two(if we are lucky) good, well written dramadies/ regular drama. Then the rest is reality shows and other crap. It seems to me that four, maybe five seasons is the magic number. With BSG, we see that full story can be told within four seasons. I would have lked to have seen a fifth season of BSG and Enterprise. So maybe somewhere around four or five seasons is all we can handle anymore. Three seasons or less seems too short and once you get into seasons six and seven things seem worn out. Now I wouldnt apply that to animated shows and most comedies.