Who could have ever guessed that this was the main character written by a homeschooled teenager?
If you want to be charitable, you could say that it provides a great example of how to completely squander both the rich plotting and characterization of the original novel and simultaneously turn your built-in fan base into an army of detractors. The Eragon books aren't perfect, and a lot of that has to do with the fact that the author wrote them at an age when most people are grumbling about the prospect of a 500-word essay. But they deserved better than to be turned into the lamest things to ever involve dragons. It's really hard to make something dragon-related that isn't either insane or great, meaning that the people behind Eragon went out of their way to create a movie that played like the director's parents had once been eaten by dragons.
The movie did still manage to make money, though, so studios might be willing to take another crack at it eventually, with "eventually" being the key word here. Hollywood is coming off the tail end of pumping out movies about a special teenage person that does something special, so we'll probably have to wait a while for it. And we'll also have to wait for the right screenwriter to come along, because it's so easy to read Eragon and think "Oh, so I'll just do a Hunger Games thing, but with flying lizards. This should be simple. Bring me my laptop and fill up the kiddie pool with gold coins and champagne. Daddy's got 'writing' to do."