Having read the books beforehand, and really liking them, I advise that you do not watch this film - it will destroy the books.
The story moves too fast and overall the whole experience of the film was pretty mediocre. The acting wasn't bad, the Eragon actor carried off the character from the book pretty well but certain scenes (for example Saphira growing up, the relationship between Brom and Eragon) were dealt with in a few minutes, depicting many, many pages in the books and so after reading the books the entire film seems very rushed.
The open ending made it possible for a sequel - of which I very much doubt will happen as the majority of people who watched 'Eragon' did so on the basis of hearing good reviews/reading the books.
From Lord of the Rings' adaptation into a very succesful film series, we all do know that decent book to film adaptations can be made - but Eragon is really not a good example of that. At all.
On a good note, younger audiences do and will enjoy the film (I have proof) and it is for this reason that i ahve rated the film a 2 star intead of a 1 star rating.
My advice, Read the books, Enjoy the books and send the film to a young child, or a unwitting stranger.