I think there's some truth to it, saddly. I haven't seen a lot of series that went past season 6 and still were as good as when they started. There are so many issues that come in the way, season after season. Most of them are listed in this article. The main problem, I think, is the fact that the cast and crew get bored a long time before the audience gets bored. Which means… actors leaving the show, being replaced by totally uninteresting actors, writers and creators leaving the show to start some new one, the scripts starting to be either convoluted, far-fetched or too lazy…

I'm not saying it's always like that. But… very often.

I'd rather have only 5 or 6 very good seasons of Castle, and let the show end on a good note, with good plotlines, good character developments, good ending, rather than a 7th, 8th or 9th season with average scripts, that would eventually ruin the show.

Notable exception to the fairly accurate "graph" would be MASH. The longer the show was on the better the episodes got (mostly). 

Granted Castle is still in the the early stages (in September when new episodes start up again we will really be only about half way through season 2). Both MASH and Castle are not fully Dramas or Comedies. Both have terrific leads and interesting supporting casts. Both are character based – normal people working in difficult situations and making the best of it. MASH survived several major cast changes and character evolution over its run. Hopefully Castle will have a long and interesting run too. 

There's a grain of truth to the article, unfortunately.  Here's hoping that Andrew Marlowe and Co. can avoid the pitfalls.

Best thread ever. lol.

By the way, I should really give credit to http://www.cracked.com. That's where I found the picture!

jrabbit said:

Notable exception to the fairly accurate "graph" would be MASH. The longer the show was on the better the episodes got (mostly). 

Granted Castle is still in the the early stages (in September when new episodes start up again we will really be only about half way through season 2). Both MASH and Castle are not fully Dramas or Comedies. Both have terrific leads and interesting supporting casts. Both are character based – normal people working in difficult situations and making the best of it. MASH survived several major cast changes and character evolution over its run. Hopefully Castle will have a long and interesting run too. 

I thought MASH plummeted in quality after about 5 seasons, after Frank left. It got too maudlin and serious when Alan Alda became one of the producers. One show where I would say this doesn't fit at all would be the West Wing. The first two seasons were amazing, and the quality slowed dropped through seasons 3 and 4, before the nadir of season 5. After that, it began to climb again.

Anyway, this 'cautionary tale' is pretty spot on for more than a couple of shows I can think of. Some even hit those plateaus and crashed down the other side well before season 4. There is a danger, with a character like Richard Castle, to twist his various character beats to extremes to fit increasingly ridiculous plots, so the writers really do have to be careful with this show.