It’s possible that Spiritwalker would have been more successful as a book, given the need to thoroughly explain events and motivations. As it exists now, condensed into a movie, it simply doesn't make sense. The protagonist shifts between identities repeatedly while attempting to regain his original self. Experiencing this creates significant mental discomfort for the audience, and that’s putting it mildly. You begin to understand a character only to have him unexpectedly transform into someone different. The acting is reliably strong, as is often the case with South Korean films. The action sequences are also well-executed; there's nothing wrong with them. Ultimately, some concepts translate effectively while others don’t. In my opinion, this falls into the latter category.

Source on TMDB