It should come as no surprise that when an 8-year-old boy is given the choice between Eragon and Charlotte's Web, it is nearly inevitable that he will choose Eragon. I see this as a very healthy interest for the young--action, excitement, adventure. It should also come as no surprise that their middle-aged fathers would far prefer the gentle remembrance of youthful reading, especially when the reviews for Eragon were so tepid.
So, what of Eragon? It's faults are faults that every reasonable child will overlook, and every adult whose chief interest is the happiness of that child can deal with readily. The movie is precisely what one would expect of a movie made from a highly derivative novel written by a 15 year-old boy. Every plot turn is not only expected, but is directly mappable to something you've seen elsewhere. There are youthful romantic notions of what it means to die with dignity. There is a Sauraman-like evil wizard who commands groups of made-from the Earth nasties whose chief job is to hunt down the hero and kill him. There are several references to Star Wars, one in the death of Eragon's Uncle another in the mysterious mentor who helps Eragon become a dragon-rider.
I won't go on with the catalogue, these illustrate the point. The movie takes bits and pieces of nearly every prominent action/adventure/mythic movie made in the last 30 years and compounds them into a unique film. Was it good? Well, let's say that it was as good as a film of this description could possibly be. The dragon-riding was probable and well-done, the acting mostly passable. It was not a fantastic film, but given its source material, that would be much to expect.
It was sufficient to entertain, entrance, captivate, and otherwise stimulate the mind and imagination of an eight-year-old boy. And so, it served its purpose well. Is it as good as other films that might do the same? Probably not. But this is one of those matters that is judged by the instance, not by the entire literature of film. In this instance, it performed to a magnificent degree the task set before it. It made an 8-year-old boy, and thus his father, very happy for a short time. It isn't a saga for the ages, but it is a saga for age 8.