If you took all the dragon-centered movies ever made, and counted the good ones on your fingers, I bet you’d still have enough fingers left over to flip off “Eragon” as you walked laughing from the theater.

I haven’t read the book, but I know this about it: It was written by a home-schooled, fantasy-obsessed teenager named Christopher Paolini and published when he was 19. And yet somehow — and this is stunning — somehow the story turns out to be geeky, simple-minded and shamelessly derivative of “Lord of the Rings” and “Star Wars.” Why, it’s almost as if … as if a home-schooled, fantasy-obsessed teenager wrote it!

The LOTR and SW rip-offs in the film are so obvious that a quick Googling shows them to have been mentioned by nearly everyone who has discussed the movie. The parallels are so plain that pointing them out isn’t even a matter of opinion. It’s like saying the movie is in color.

The story is set in the forested land of Alagaesia, where 17-year-old Eragon (Edward Speleers) discovers a big blue jelly bean that eventually hatches and produces a dragon. There used to be dragons all over the place here, in the old days, ridden by noble knight-warriors who used them to do good and spread peace. But then the evil Galbatorix (a campy John Malkovich) killed them all (kill a rider, his dragon dies too) and yoked the land under his oppressive rule.

So now Eragon has a dragon named Saphira whose thoughts he can hear in the voice of Rachel Weisz and who is loyal to him as her rider. Eragon finds the village crazy person, Brom (Jeremy Irons), who Obi-Wans him with training and backstory, and they set out to join the anti-Galbatorix resistance forces gathering in the mountains. But first Eragon wants to save Arya (Sienna Guillory), a woman with whom he has an unexplained psychic connection and who stole the dragon egg from the king in the first place, from the clutches of the king’s villainous henchman Durza (Robert Carlyle).

The book represents the first part of a planned trilogy (part two has been published already), and it shows, sloppily, in the way the film is assembled, with characters and subplots introduced or hinted at and then ignored, presumably to be completed in the next installments. Eragon has a cousin in the first scenes who then disappears for the duration; Eragon was abandoned by his mother years ago, yet that issue is not resolved; a new character shows up late in the game to fight on Eragon’s side, but his importance obviously won’t be realized until later chapters.

A good movie would deploy these foreshadowy elements more subtly, or meld them in more seamlessly with the central action — anything to keep them from sticking out like sore thumbs. This movie, adapted by Peter Buchman (“Jurassic Park III”) and directed by special-effects technician Stefen Fangmeier, just throws everything in. The result is a head-scratcher of a flick that looks like it had scenes deleted.

I suspect earnest fantasy buffs will be more disappointed in it than the average person, who will only be mildly disappointed. The story has the form of “Lord of the Rings” and “Star Wars” (oh, and Harry Potter), but it lacks the depth and the universal themes of those sagas. Those stories are about fantastical things but have underlying complexities that are down-to-earth and relatable. “Eragon” has no such weight. It’s a silly story about a teenager riding a dragon, and absolutely nothing more than that.

C- (1 hr., 44 min.; PG, though it has rather a lot of violence for a PG movie -- should be PG-13.)