I maintain that this is a charming book that indicated great potential for the rest of the Inheritance series, and for his career as a writer. Paolini certainly betrays his youth and naivete by basically lifting his entire plot from Star Wars and The Lord of the Rings (with some minor variations), but he also comes off young and energetic, and that kind of tone is infectious.
Unfortunately, something goes wrong between the publication of Eragon and the publication of Eldest. The story becomes bloated and self-congratulatory, and as a result, the unintended plagiarism and plethora of cliches becomes too much to deal with. Maybe once Paolini has gotten this series out of his system and gets the chance to grow up a little, he'll churn out something that lives up to his initial promise.