When I finished the Riyria Revelations most of the puzzles and ideas were properly filled in for me, except for the full story of how Royce and Hadrian met and what some of their other exploits were. In the two books in the Riyria Chronicles, the rest of these gaps have been filled in, leading to a full set of Riyria stories which complete the entire world nicely. Personally, while it would be nice to get more of Royce and Hadrian I feel that these two novels adequately complete their story arc and that any concluding stories would be impeding on a good thing and trying to milk a marketable good rather than necessarily existing as a piece of art. But if the right story does exist I challenge Michael Sullivan to prove me wrong! Personally I'd just love to see a story set in the future following descendants of these individuals...
So I don't think I can say too much without spoiling the plot. Let me say that it is a wonderful plot: full of twists, turns and little surprises that all tie into the beginning of Theft of Swords nicely and yet stand alone in their own right. I feel that these books are perfect prequels because I could imagine reading them in order chronologically or as published and still loving them all the same. For what I feel I can say is that the book does include the short story The Viscount and the Witch and builds on from there into a plot featuring vengeance enacted by Royce, mistakes made naively by Hadrian, rescues of damsels and thefts of earrings... But the greatest part of the plot involves a plan to murder the royal family.
The wonder of this book is that for the aware reader one can see how the characters progress to the point of becoming the Riyria you see in Theft of Swords. This sense of progress instils the idea that this is an organic and almost real world (if you took out the ). For all its aims to stick to a more traditional fantasy route, this story ends up appearing more realistic than many of those gritty fantasies out there populating the market now.
I said before, and let me use this again to conclude, that this book is made strong by its characters. The description and worldbuilding is strong enough with its mix of colloquialism and tight phrasing but it is the dialogue and character building that makes this book addictive and readable. So, it should not need to be said, but if you are a fan of the original books read these. And if you are looking for something new in the fantasy world to read then take a look at these.