Going on to the plot, I loved how everything tied together from beginning to end, as if the writers went into this with a solid idea of where they were going. Everyone has complexity here, there aren't any of the usual 1-D villains and annoyances. I LOVE that about the show and wish more dramas would create realistic, likeable side characters in place of the typical in-your-face obvious second leads. Moving on to the second leads - I can't really say anyone except Se Joon is a true second lead, and he doesn't stay that way for very long (he moves on to his own love line).
Instead, they are forced to know and comprehend one another, and unwittingly fall in love along the way. If he hadn't gone through with his plan for justice, or if the source situation had never emerged, these two people would likely have remained strangers for the rest of their lives. And a wonderfully unique premise in a land where "fate" and cliches abound onscreen. In Woo's actions, while a bit extreme, perfectly exemplify the idea of creating one's own destiny.
Sounds weird, but was fascinating to watch, especially this second time around, when I already knew and understood In Woo's inner motivations. Instead, every meeting was pre-orchestrated by our guy, all for a believable and understandable secret cause that justifies and ties it all together at the end.