I found Bundori to be a frustrating book, but not because of the writing, or the story, or the plot points. It was frustrating because Sano was frustrated by Bushido, the set of principles, traditions, and customs that samuari were expected to adhere to. Sano's investigation was hampered by Bushido, his love life was hampered by Bushido, his friendships, lifestyle, even his acceptance by other samuari and his place in the Shogun's employ are all hampered by Bushido. Poor Sano can't catch a break, and while success does come to him as a samuari, he becomes more and more unhappy in his personal life, and more disillusioned with the path his professional life is on as his fortunes and his status improve. That's frustrating to have success with no happiness, and Rowland does an excellent job of conveying Sano's feelings to her readers.
This is a book that you know very quickly is not going to have a happily ever after ending. Sano knows it, too, and still he does his duty, not trying to fight the desolation he knows will come at the end of this adventure. Sano's strength of character keeps the reader moving with him to his unsatisfying fate. In a world where almost everyone is desperately eager to only align themselves with individuals who are currently in favor with the elite, it doesn't seem right to waiver from Sano's side as he does his duty. So, the reader's heart breaks along with his, even as he achieves glory and favor from his lord. This is fine writing, and a story that is beautiful in its bleakness.