It has proven to be as enduring as an Everlasting Gobstopper, as fun as Exploding Candy, as mysterious as a Snozberry. It's not a Christmas movie, but Christmas wouldn't quite be the right without at least one viewing of Willy Wonka and the Chocolate Factory. And there it is, tucked into the Christmas Day schedules. Forget Christmas dinner. We'll have a Three-Course Dinner Chewing Gum instead, writes Shane Hegarty

It was an Americanised version of Roald Dahl's book about a boy in a legendary chocolate factory, and was financed by a food company hoping to sell a few tie-in chocolate bars, but it went on to do poorly at the box office. Dahl hated it, not least because his original script was considered too faithful to the book and re-written by the guy who went on to write The Omen. Tim Burton isn't crazy about it either, so he's remaking it this year, with Johnny Depp as Wonka.

"I don't want to crush people's childhood dreams, but the original film is sappy." He reckons that Chitty Chitty Bang Bang is a better flick. Considering what a mess he made of his "re-imagining" of Planet of the Apes, he should be careful what he says, in case some ironically horrible fate befalls him, just as it did Violet Beauregarde, Mike Teevee, Augustus Gloop and Veruca Salt.

But there are a lot of people who do love it, and it has become one of the great cult classics. A kids' movie pored over by adults. They love the look, sound and taste of it. They love the creativity behind this (literally) delicious morality tale, and how it contains as much bitterness as it does sweetness.

They love Gene Wilder playing a character who lies, tortures and shows utter disregard for the safety of children. His hair says it all. It starts off relatively calm, but by the end has become quite wild. In the final minutes he screams and yells and berates the boy hero Charlie Bucket and his grandfather. He treats them with contempt, kicks them out. Then, when Charlie hands back the stolen gobstopper, Wonka embraces him. He tells him how wonderful he his. And then he gives him the entire factory. The man, we realise, is clearly mad.

It reflects a split personality that makes the movie so fascinating. It has been described as "like The Wizard of Oz on drugs", which is a bit of an overstatement, but it has its obvious moments of overt psychedelia, such as when the parents eat from a giant polka-dot mushroom.

But it also makes for discomfiting viewing. Apart from those scenes of Wonka losing his temper, there are moments of deep terror that take it out of standard kids' territory and into the realm of horror. When they take Wonka's boat into the tunnel, they are treated to images of chickens being beheaded, a snake crawling over a man's face, large eyes and the terrifying Mr Slugworth. I need to check the DVD version, but I could swear there's porn in there too. All while Wonka goes into some crazy mantra. If it is psychedelic, then this is the bad trip.

It is one of the many things in the film that leaves you guessing. For example, what exactly is Wonka's relationship with the Oompa-Loompas? He says that he rescued them from danger, but are they now slaves? Are they unionised? Why no female Oompa-Loompas? And how economically viable is an Everlasting Gobstopper anyway? Or giant bars that can be shrunk and sent through television sets, via Wonkavision? And is the Fizzly Lifting Drink not likely to send kids floating off over oceans, or the Exploding Candy something terrorists would want to get their hands on?

Burton doesn't think that the original is dark enough. The new movie poster features Depp as Wonka, pale face half-hidden below a ragged top hat. It's a little like Edward Chocolatehands.

The book, Charlie and the Chocolate Factory, caused a stir when it was first published. Librarians, unhappy with its happy contempt for much of the human race, refused to keep it on their shelves. That was not the only contentious thing in it. Burton may refer to the book, but he'll skip the part in which the Oompa-Loompas were originally black pygmy workers. Dahl changed that in 1973, when he made them white with long brown hair. The movie, of course, made them orange and green.

The story was inspired, according to Dahl, by a brief stint testing Cadbury's chocolate while at school, and it was typical of a children's writer whose warped imagination is being rediscovered by Hollywood, which this year is turning to his books as never before. The Fantastic Mr Fox and The Twits should follow soon.

In the meantime, this is the last Christmas when fans can watch the movie untainted by a remake. They have already survived Nestlé's marketing of real-life Wonka Bars, which taste nowhere near as magical and hysteria-inducing as the ones bitten into by Charlie Bucket.

But the original should survive all that and most likely continue to get brighter with age. A film of pure imagination in which children and their horrible parents learn lessons about gluttony, greed, materialism and addiction to television. Perhaps it is about Christmas after all.

Willy Wonka and the Chocolate Factory, starring Gene Wilder, is on TG4 at 9 a.m. on Christmas Day