He was, all in all, a benevolent ruler, but I don't find him all that ethical at a personal level. e.g.
- The way he dealt with Oboi wasn't particularly honourable.
- When WXB 'rescued' the 3 members of the Mu family, KX suggested that he kill a few royal guards in front of them to earn their trust. WXB took pity on the guards, and when some of the Empress Dowager's eunuchs conveniently turned up to take him, he substituted them instead.
- He didn't bat an eyelid at hearing WXB killing the real Xiaoguizi or lying about killing off a maid.
- He completely ignored what his father said about the Manchus retreating to where they came from if they could not be of benefit to the population (to his credit, his rule did benefit them, but he obviously meant to stay whether or not they were, out of ambition). He also tried to burn his bridges by destroying the 42 sutras (not a wise move in retrospect, considering what happened to the Qing dynasty later).
- He actually felt thankful to the fake empress dowager for killing off Consort Donggo and her son and thereby paving his way to becoming emperor, despite her killing off his true mother, driving away his father and imprisoning the real Empress Dowager. To his credit though, he didn't let himself think too deeply along those lines.
One of the themes of DOMD is the balance between Kang Xi the person and Kang Xi the emperor, and in the relationship between WXB and KX as both personal friend and ruler-subject. In both cases, there is a marked slide towards the latter in both cases as the story progresses until it becomes the dominant factor with only a vestige of the former remaining. This is generally not dealt with well in adaptations.