...I can't believe someone rated this as "Illiterate". o_O
I'm a fan of this pairing (they weren't RAISED as brothers, darn it!), so I'm pleased to find someone like-minded. You seem to have a good grasp on their characters--I particularly like the line about Murtagh examining his emotions as though they're wounds--nuisances, things he cannot help--it fits with him. He's used to being on his own, used to knowing himself very well, I think. Sadly, I'm 100% sure Eragon will end up with Arya; whether the romance will be CONVINCING is another thing altogether. But I digress.
More, please! You've done your vignette, now give us some action! Perhaps something set during Eldest? :D