If you’ve gotten through both Eragon and Eldest and you are still interested in reading Brisingr, it is unlikely that my opinion will sway you either way. For me though, Brisingr is where the Inheritance Cycle started to slip from mediocre to bad. 

In the first place, I think Brisingr and Eldest aren’t fundamentally different stories (I keep forgetting in which order events occurred), and should probably have been a single book, as was originally planned. There is a lot of extra plot in Brisingr – especially the Ra’zac quest, most of Roran’s story line, and the sub-plot with Galbatorix’s supersoldiers – that add to the page count without bringing the story much further. There are some reveals in this book that feel like they should have occurred in the second installment, and Eragon moves all over the world to be places the plot requires him to be. Brisingr feels ‘inefficiëntly’ written, and maybe an editor should have cut most of it. 

Secondly, there are a couple of questionable choices that drive the rest of the Cycle – such as Roran’s superhuman killing power, the waste of the first part of Celembum’s prophecy, and the reduction of dragons to Pokémon through the Eldunari system. It may be that I wasn’t as positively disposed towards the series at this point, but these kinds of decisions took away the hope I had that the series would improve with Paolini’s age. It sadly didn’t, and I would discourage most readers from spending their time on Brisingr.