Goofs

When Arya shows the Saphira's armor to Eragon, the armor is very different than the armor that Saphira wears later - especially the helmet.

When Brom and Eragon are riding to Daret, it can clearly be seen that Brom is leading the way. Then, in a shot when the camera flies over the two riders from behind, it is Murtagh riding instead of Brom. You can tell by the larger cape, longer hair, and the fact that he is carrying a bow, which Brom never had. Then in the next shot it is Brom again.

Eragon leaves his home without his bow, but later on in the story he suddenly has it again.

When Eragon takes his first flight in Saphira's saddle, Brom follows them by horse, alone. Towards the end of the flight, he is leading Eragon's horse.

When Eragon first realizes that Saphira is hungry his hand is not wrapped up, but when he withdraws his hand from around a corner holding the skin of milk, it is suddenly bandaged.

About 40 minutes in the movie, during a riding scene, the CGI hills in the background are not synced correctly to the camera motion, giving the impression that the hills are actually moving against the foreground.

At the end of the movie the King is seen taking a sword and drawing it. His nail is seen bending like soft rubber as he does so.

Some of the pants worn by characters in the film are very obviously modern and out-of-place looking blue jeans.

When Brom and Eragon stop and get off their horses (after fleeing the Ra'zac, before Brom inspects Saphira), both can be heard referring to Saphira as "her" once and "she" three times during their dialogue. However, both of the characters clearly mouth the words "him" and "he". The sound was obviously re-dubbed. Additionally, there are one or two instances of missed dubbing, and either clearly refer to Saphira with male pronouns.

Eragon taps the dragon egg, and it makes the sound of a hollow metal pan, even though it's not a metallic object.

When Eragon wakes up from one of his visions with Arya, there is a pair of legs behind him. The camera turns away to face Brom, and when it returns, the legs are gone.

How did Brom get to Durza's castle in time to save Eragon? He left to go rescue Arya on Saphira, and flew over various mountain ranges to reach the castle, yet Brom somehow caught up to him with only a horse as transportation. Actor Jeremy Irons actually asked Stefan Fangmeier this question too (according to the audio commentary) and Fangmeier hand-waved it by explaining that the audience wouldn't notice. In the novel, Eragon was actually captured by Durza and held prisoner for a few days, which is how Brom caught up to him.

How did Eragon know how to use a spell to unlock Arya's cell? Brom never taught him that spell.

Saphira, in the film's narrative, has only existed for a month after hatching, yet she somehow knows way more about the world than Eragon, a 17 year old, does. The novel explains that dragons inherit genetic memory from the dragons that came before them, but such an explanation is not given in the film, so it comes across like she has this knowledge for no discernible reason.

Where did Eragon get the disguise that he used to sneak into Durza's castle?

How does Durza know Eragon has the dragon egg? Arya told him the egg hatched but she never told him Eragon found it, so unless Durza read her mind, then there's no way he could know Eragon has it.

Brom suggests Saphira fly into the sky as a lookout while he and Eragon look for the Varden. This is actually a bad idea, because Saphira's presence could alert the Urgals to their location, which is exactly what happens.

Eragon and Saphira seem surprised to find out Brom is a former dragon rider upon seeing his scar, even though he had already displayed tremendous knowledge about dragons and riders.

Why didn't the Razac simply hide somewhere and wait for Eragon to return home to kill him after killing his uncle? He disappears after the attack, seemingly abandoning his mission.

Angela, a fortune teller, tells Eragon that someone he knows will die in the future. For some reason, Eragon thinks she's talking about his uncle even though he already died.

Durza stabs the captain of the Urgals in the foot before ordering him to find Eragon. That wouldn't be easy for him to do if he has a foot injury.