Lee Junho's performance was exceptional. He just keeps getting better with each role. However, the FL's role, whether by design or not, was inconsistent and left unanswered questions as to her motivations. The first half of the series, she was an interesting character, one you could understand being attractive to the ML, but later when her attitude changes, and she grow cold and unapproachable, the reason given just doesn't seem enough. His love sours and turns into obsession and he struggles with his choices. But she doesn't and that seems unrealistic. That said, I have rewatched this and will do so again I'm sure. But that's because of Junho's stellar performance.
Review of Red Sleeve
