I really enjoyed this author's Riyria Revelations series. He quickly became a favorite author of mine after I discovered him. I love his characters and their development, as well as the twists and... ahem... revelations that come along in the plot.
The Rose and the Thorn, along with its predecessor, The Crown Tower, are prequels to the Revelations series. Revelations had what I felt was just about a perfect ending, and I agree with the author's decision not to interfere with that. It was this that led him to begin writing prequels about Hadrian and Royce.
A problem that comes with prequels, that I feel these books faced, is knowing where things are going to have to wind up by the end. I felt a great deal less suspense, reading this plot, knowing who the real villain was. Knowing already what certain characters were secretly up to did take away from this for me.
As a stand-alone book, I think this is a really enjoyable story. I still want to see more from this author. What I would really love would be if he wrote something really new, either completely unrelated to this setting, or several years in the future. Or if he still wants to keep writing about Hadrian and Royce, perhaps find new snapshots of their past that the readers will not already know the outcomes for, that can still stand on their own without weakening the later installments. That said, I wouldn't be able to resist reading it if he put out another Hadrian and Royce prequel.
I do still highly recommend this author, and will continue to enthusiastically read whatever he writes.