A bit like Brisingr, you get the feeling with this book that if someone ripped 200-300 pages out of it and stapled them together you could get a fantastic, exciting story. Sadly, the author has wrapped this up in 500+ pages of irrelevance, almost as if, just like Eragon, we're all a little bit scared of getting to the final battle and want to put it off as long as possible. This is a shame, if you cut out the pointless sub-plots, needless musings and unnecessary clarifications there is a story as good as Eragon or Eldest hidden beneath.
I am surprised by how many people disliked the ending of this book and the climax of the series, for me that was the best bit. The way Eragon finally defeats the King is clever, unexpected and plausible, none of which was expected given the huge difference in their ability levels, time and again alluded to in the books.
Also, although some story arcs are wrapped up with neat little bows, not everything is left so clear cut. Being sickened many authors 'happily ever after' obsession I was delighted Paolini didn't fall into this trap.
If you've read the last three books you should definitely read this, it is it's own sweet form of torture, but like running your first marathon, you'll be happy you put yourself through it.