I read all three of them half a year back in one fell swoop. I remember buying Brisingr because the name and picture looked cool. At home I read that it was the third book so I first had to buy the other 2 books...which took my quite some time xd
That was the original intention, but the first movie completely failed (with reason) so they decided not to go further.
It has nothing to do with that =/ he was planning to make a trilogy, however while he was writing Brisingr he came to the realisation it would be to much to fit it all in just Brisingr, so he decided to make a fourth book. With other words a lot of parts that were originally intended to be in Brisingr are now going to be in the fourth book. The result was that he had to edit Brisingr too as every book has to have a storyline that builds up to the end, whether it's a trilogy or not, so he had to change things. The climax with the shade at the end of Brisingr was something he added just because he needed something.
The entire fantasy-genre looks the same as the same things keep repeating themselves: alternative universe, dragons, elfs, dwarfs, some villainous race (orcs, goblins, urgals) etc. though that doesn't make it plagiarism.
Overall seen I was able to read all the books, so that instantly means it got my imagination going, otherwise I would have stopped reading them. The books had something, however they can't compare to Harry Potter and certainly not to Lord of the Rings. Paolini really just makes it up while writing it. There are a lot of truly weird scene's or twists in the books which are just dull and don't help the story at all.