I think that calling it a ripoff isn't fair. I've done some courses and whatnot in writing and there's a general consensus that all stories have been done already. Example: Take the main characters from Dune (movie version here since it's been too long since I last read the book) and the first Matrix movie. I'd like to add that the two movies are different enough that I somewhat doubt Matrix was a ripoff. The later two are a bit different in that regard
Both main characters are the result of a breeding program, both are unnaturally skilled at the tasks and abilities required in a culture/world that they are thrust into, both are accepted as a great and important man within their new culture almost immediately, both die and come back more more powerful and in so doing gain the ability to see beyond the veil (albeit meaning different things to each), and both end up changing their world.
And any resemblance to Jesus anywhere along that path is most certainly not coincidental.
The trick is to tell the story with a twist or as I've learned to call it 'a kink in its tail.'
Now then: Is Eragon a ripoff? I don't think so. Heavily influenced, definitely, but I don't see it as a ripoff. That said, I didn't like it, though I only read the first. Easy read, but the main character is a Mary Sue. Or Gary Stu, I guess.
A random farmboy becoming a great mage (greater than the teachers at the resistance base, though not better than the Elven Princess who takes him as an almost protege and rushes to his rescue when these jealous mages try to goad him) and a master swordsman in a few months; most of this time spend travelling, and not hard training. He also learned the Master Language in the same time, making him a great speaker who can be understood by every animal in the world, including packmules.
It wasn't, however, until the world-weary, hard, embitterned King of the Dwarves broke down in tears in the middle of a horrific battle at the sheer MAJESTY of the boy's combat ability and courage that I (to paraphrase Yahtzee) noticed the words Author Surrogate written across the sky in blazing green letters.
Bottom line, if you enjoyed the books, more power to you. However, Eragon is neither the first, nor anywhere near the best book for a story of that genre, in my opinion. Take that for what it's worth.