Let me first say that when I heard they were making a movie Eragon, I assumed they were taking the Lord of the Rings or Chronicles of Narnia route. I figured they would try to stick as close to the original text as possible, but alas I was quite wrong.
If you are a fan of the book, you will probably hate the movie. The first problem is the length of the movie. I was expecting two and a half hours, not 108 minutes or whatever it was. I understood the need to cut out some things, I am usually fine with that. In fact, I am usually the first person who says you should not compare movies to books. But, this movie ignored most of the major things from the book, not just the little things. For example, the Urgals in the books are monsteresque. They are big, black, and have giant horns. It was like Fox did not want to fork out the money for a makeup crew.
I will not go into the entire differences between movie and book, but I will say one of the things I really like was the chick who played Arya. In the book, I never got the impression she was hot (maybe it was her icy personality, she is an elf afterall), but in the movie, well let me just say "Damn!"
This movie would be good to take children or even a chick, especially if they have not read the book. They will find the young Sapphira to be supercute and will probably prompt you to try and buy them a dragon.