Not that Prince Rashko eschews competence; although he values his intellect highly (especially since he views himself as the only member of his family with a functioning brain) he also lets the reader know that's he's a big, strong, athletic swordsman, just like his simple-minded brother. And despite his towering intellect, he also rarely sees through to the meanings of the folksy proverbs scattered about by his father and other mentors.
The bad guys were suitably menacing, from the casual cruelties of the retainers to the magical attacks of the visiting prince and his beautiful daughter. Although I suspected from the first that Rashko severely underestimated the comprehension of his relatives, I liked how the entire family loved, trusted, and respected each other even when using vastly different tactics. The frequent intermissions to show the legend of Prince Pavol and the founding of the castle help build the themes of the story without slowing down the suspense.
My seventh grader also liked the book; the dragon and castle cover with its gently creepy color scheme enticed him to pick it up a few weeks ago. I'll see if the fifth grader wants to try it. (Nope)