I think most shows have about 3-5 good years in them. There are exceptions, I suppose, but after that much time, your average cop/medical/legal drama and family/edgy sitcoms have said about all they can reasonably say on their related subject matter, cases, adventures, misunderstandings, etc.
As much as I love watching
Law & Order, the fact is that show just churns out the same 6-8 storylines, updating the details to tie in with modern outlooks/events, or “from the headlines” aspects while updating the cop and lawyer roles every few years as well. It's warm comfort food, but even when I stumble across an episode I've never seen, I can pretty much predict/lay out the entire following 55 minutes.
I can’t think of any show - any genre - that somehow got
better, or
more watchable/dialed-in, after season 4-5. Just doesn’t happen. Retreads and running-out-of-ideas is unavoidable, and that's when you start to see the "out there" ideas/plotlines (aliens and demonic possession on shows where such a thing should never occur
), the stunt-casting, bringing old characters back (even if they died three seasons ago), crossovers, spin-offs, the cliffhanger two-parters and all the other mako-leaping silliness TV shows fall into once they've shot their creative wad.
There should be some sort of Hollywood TV law...you got five years to say all you can/need, then beat it!
