Last night another series of Top Gear came to an end – set to be remembered as The One Where Richard Hammond Said Something Hateful About The Mexicans. But, while everyone has been busy getting their knickers in a twist about a man with silly hair being deliberately offensive, they've missed another quite important point made clear by this series. Top Gear simply isn't as good as it used to be.

There was a time when the show used to be something close to event television – a time for all the family to gather round and watch three paunchy old morons blow stuff up for an hour. It was a Generic Jackass, an It's a Knockout with Audis. But somewhere along the line, the sparkle went missing. At some point, blokey innovation gave way to grinding repetition.

I'm not the only person I know who tends to watch Top Gear on iPlayer now. Once you've skipped all the bits that are identical every single week – the by-the-numbers car reviews (the host shows us a car he likes, then another car that he prefers to the first car, then plays the soundtrack to a Christopher Nolan film while he drives them both around), the lap times, the bit where Jeremy Clarkson introduces The Stig in a funny way and the all the Stars In A Reasonably Priced Car that don't involve John Prescott – you can usually plough through an episode in about 20 minutes. If you've skipped all the bits where the presenters behaved dubiously around foreigners as well, you could probably squeeze the whole series into a medium-length toilet break.

It's hard to pinpoint the moment that things started going awry. Certainly some of the magic rubbed off when it transpired that several of the Top Gear stunts weren't quite as spontaneous as they seemed, but the blame could just as easily lay elsewhere. The presenters haven't gleefully laid into the government as much since the Tories were elected, and the whole palaver over the unmasking of The Stig put a permanent blot on the Top Gear copybook. And then there's Hammond's haircut which, despite being carved into a marginally more acceptable shape several months ago, remains an intolerable crime against all of humanity.

But the main problem seems to be the show's gnawing lack of imagination. While the challenges are still the highpoint of each episode – this series alone we've seen combine harvesters converted into snowploughs, luxury cars being driven through Albania and several second-hand BMWs being tested to destruction – everything else has become flabby and formulaic. This version of Top Gear will never be as buttock-numbingly dull as old Quentin Wilson-era Top Gear, but it's a shadow of the show it was four or five years ago.

There's still fun to be had, of course. Last night's moon buggy segment demonstrated a nice change of pace and Jeremy Clarkson can be a thoughtful and compelling broadcaster when he chooses to be, but the reliance on the same three or four items is slowly dragging the whole show down. If Top Gear can put as much effort into keeping itself fresh as it can into blurting out thoughtless insults about people from arbitrarily chosen countries, then we might have a decent show on our hands again.