How funny is it? Imagine the best bits of all your favourite Simpsons episodes rolled into an 87-minute package. Then add a sensational skateboarding session from a naked Bart, a hilarious guest spot from Green Day, and Homer's pet "spider pig".

If you've seen the trailer, you'll know what we're talking about. And they're just some of the film's many highlights.

The Simpsons Movie succeeds by keeping things simple. From those familiar opening credits, it feels like you're pulling on a pair of comfy slippers and settling in for an extended episode of the telly show. That's not a bad thing.

Surprisingly, director David Silverman doesn't take advantage of the benefits of hitting the big screen. There's no swearing, and only a little nudity - this is not South Park: Bigger, Longer, Uncut.

But The Simpsons Movie has to be rated on the laughs factor, and they come thick and fast. Along with the usual targets - religion, war, American politics and Fox - director David Silverman and creator Matt Groening also find a few new ones.

The film opens with Groening having his own little laugh at the audience: Homer stands up during an Itchy and Scratchy film screening to ask "why would we pay for something we already get to see for free on TV?", before calling the audience "giant suckers". Nice.

Without giving too many spoilers away, the plot centres around an environmental disaster that could spell the end of Springfield.

Along the way, there's romance in store for Lisa, marriage problems for Homer and Marge, a giant plastic dome placed over Springfield and Bart tries to join the Flanders clan.

But, like the show, it's the little things that make The Simpsons Movie so enjoyable. Like the none-too-subtle digs at Al Gore's An Inconvenient Truth, Homer's constant quips about Ned Flanders' sexuality, and - of course - the spider pig.

It also harks back to the golden age of The Simpsons by referencing classic episodes. Remember the three-eyed fish? What about Bart's dare-devil skateboarding run? They're all here - but bigger, bolder and funnier.

And - impressively - almost every character gets screen time, from Bumblebee Man to dodgy doctor Nick Riviera and hillbilly Cletus. And some of the best lines are saved for Comic Book Guy and bar owner Moe.

Family Guy and South Park have long been considered to be fresher and more relevant than The Simpsons. But remember, without The Simpsons, those shows wouldn't exist.

It's a point The Simpsons Movie makes in fine style. Eighteen seasons? If it's still this good, let's hope they double it.