Opinion: The Simpsons has got to end at some point, so why not now?

The Simpsons passed into history again last night when the 636th episode was broadcast on US television, making it the longest-running prime-time scripted series - surpassing Western staple Gunsmoke by a single episode.

When you look down the list of those its surpassed, there's a recurring theme throughout and it's that they're all very much of their time. Lassie, Bonanza, Kraft Television Theatre, even Law & Order and Law & Order: SVU are pretty much old hand at this stage and The Simpsons is no different. Even leaving aside the furore surrounding Apu and the manner in which it was handled, no one can reasonably say that The Simpsons is fresh and vital like it once was. In fact, where once it was leading the way in popular culture, now it's becoming reactive.

Before, you had glancing references - like Homer remarking how weird Twin Peaks was in an off-hand moment in an episode. Now you've got entire episodes built around them, crossover episodes (something they expertly skewered so many times before) and they've even taken to retconning their own history to make it so that it's moved up in time.

It may seem like a tired and dried-up cliché to say it, but The Simpsons stopped being funny and entertaining around about its eleventh season, possibly even the twelfth. It's now currently in its twenty-ninth season. By simple virtue of mathematics, that's seventeen sub-par seasons that the series has put out.

We forget sometimes that not every episode was a winner in the twelve hallowed seasons when The Simpsons was good. For example, Lisa the Skeptic from the ninth season tried in a hack-handed manner to grapple with religion and faith with an unearthed angel ultimately turning out to be a promotional tool for a shopping mall. Others, such as The Simpsons Spin-Off Showcase from the eighth season, were utterly forgettable attempts to replicate previous anthology-style episodes. There are plenty more examples, but there was always a baseline of comedy, ingenuity and knowing that's been painfully lacking from subsequent seasons.

It's not a reflection on the writing staff, either. Comedy, by its very nature, is a zero-sum business. You either laugh or you don't. It's a disposable thing. You laugh, you move on, you laugh again, you move on. It's easy to take in, but difficult to do for an indeterminate length and nobody would expect a show to be consistently brilliant after twelve seasons, let alone twenty-nine.

Given how other animated series have stolen a march on The Simpsons, the series now exists as an institution rather than as a vital cornerstone of popular culture. The very fact that sketches and brief moments have now been extrapolated to become memes - the Steamed Hams bit is a perfect example - shows that it has an elasticity beyond its years.

It's always there, and it'll always be there - but does it mean it's still good, and more importantly, is it still relevant? Absolutely not.

The merciful thing to do would be to finally put it out of its misery, safe in the knowledge that it has long since passed into the history books and allow itself some dignity in the passing. There are at least two generations of adults who grew up with The Simpsons and that's plenty, quite frankly. Be honest - when was the last time you made The Simpsons an appointment viewing? When did you last sit down to watch it with the certain knowledge that you were going to enjoy it?