Critics will loathe Eragon. I guarantee that the vast majority will slam it.
But it is actually not the disaster they say it is. In the same way that they misunderstood The Da Vinci Code movie, they will misunderstand Eragon.
The first thing they will say is: "Hey, this is a Star Wars rip-off"! Ignore their bleating. It would make sense only if you do not realize that Star Wars itself was quite possibly the most derivative film in history, if you don't count deliberate spoofs and pastiches.
Secondly, they will say: "Hey, there are elves and things, so this is a Lord of the Rings rip-off". This comment would only make sense if you did not realize that the whole sword and sorcery scene pre-dated Tolkien by many decades.
So what's the real guff about Eragon?
It's a dragons-and-fantasy story based on classical mythical elements, just as Star Wars and Lord of the Rings were, aimed at young people.
Eragon, like The Da Vinci Code, is an attempt to make a film which treads the careful line between two minefields.
If you just translate a book into a film, it doesn't work as a movie. You don't want to do that.
If you make a movie which rewrites the story, it annoys the fans of the book, who are one of your primary markets. You don't want to do that.
So you make a film which satisfies most of the people who enjoyed the book, while at the same time, having enough visual spectacle and storyflow to make the experience work independently as a movie. You make the best movie possible out of your source material.
If you can suspend your disbelief, be a kid for a while, and allow the book or movie to draw you into its immersive world, then lines such as "Tell Saphira to fly above us and scout the countryside for Urgals, or at worst Ra'zacs!" are what you expect, and make sense in context.
But if you remain a cynical adult observer, the lines are going to come across as horribly geeky and silly, especially if you take them out of context, as I have done above.
Verdict: Critics will hate it, not realizing it is not for them.
People aged 12 to 19, or imaginative adults who can get themselves into that mindset, will be deliciously lost in a fantasy world for a couple of hours and will have a great time.