my comments are specifically about the book, not the movie, "Eragon"
Indeed, Terry Brooks has created a derivative of Lord of the Rings. However, in Terry Brooks' world (granted, he has numerous books set in the world at this time), he explored and expanded the world to make it his own. One that fans are greatly committed to.
Chris Paolini has not had to opportunity to flesh out his world to the extent of established writers. With only two books written, the Eragon world still relies heavily on outside influences to support the imagery that the readers will understand and relate to.
Continuing to compare Brooks and Paolini, both have chosen the innocent hero thrust into a world-altering situation. Both employ the common themes of elves, dwarves, and dragons (to name a few). Magic is powerful, yet uncommon. To this point, I think that there is no specific plagerism or copying; these are common themes in fantasy writing.
The road to publishing may be a more interesting story. While many fantasy authors well-known today struggled in the early writing years, Paolini was able to employ a short-cut. He had his book published in a limited run by a Publishin House. Do not get me wrong, if I finished a book, I might pay to have it bound in the hopes that it would be purchased and read.
***Opinion***
Where I feel that the audience is being cheated with the Eragon franchise is that it is not being allowed to mature before packaging it for mass consumption. The world has not grown beyond the borders established by the original source material, and with the movie, it is being required to be consumed in its immature state.
What I am saying is that Eragon, as a world, is still too young to be made into a movie. That is has only underscores the fact that the story is still too close to the materials that it is derived from -- namely Star Wars, Lord of the Rings and King Arthur.
It is unfortunate that this promising fantasy world will, very likely, be cut short before it has time to reach its full potential. The movie was sub-standard as an introduction, and the books will be churned out on time rather than quality product.