I don't based my comprehension by just one word.

But yah to each his own.

Well, I hope he will end up getting the role. He has able to pull off Introverted Boss with very weak storyline and unpopular leading lady and think he will do just fine for this drama.

You must have like those one-dimensional act, shallow interpretation and simple characters common in romance dramas. Some of those kind of acts even deliver the same emotion all through out the drama and worst from one drama to another.

Well, definitely that is not LJG. Most of his characters are really complex and characters that develop in really wider range. I have only seen few actors who could pull these characters.

Though I have seen him in quite characters in few of his really old works e.g Virgin Snow and Flying Boys. Of course I could understand because he was still young back then. Thought, it wasn't bad but also not critical good. Then I think in his drama Hero... That one was a miss for me.

The only reason why I thought Hero was a miss even he did well in that; IMO because he delivered the same interpretation as what he did in the drama prior to this.

Actors are as good as their last performance. Acting is always hit and miss.
I love all the actors that you mentioned though acting performance per-se, except Gong Yoo as he does the same thing from Coffee Prince to Goblin not just the acting and expression but even the look. (Verdict- all miss for drama characters, but I love Coffee Prince for entertainment value. Thinking about it, I endured to finish Big. Now, I wouldn’t waste time on that drama.)
While many love Kill Me Heal Me, I actually preferred Hyun Bin's Jekyll and Hyde. Though I love him since Kim Sam Soon, but I must say he does not possess the same depth and versatility as LJG. (Verdict: Secret Garden was definitely a miss (this drama was too cheesy). Though I don’t the middle part of this drama but I love Hyun Bin’s performance in Jekyll & Hyde, the rest are only for entertainment value)
I notice Kim Soo Hyun since Will It Snow this Christmas. But he hasn’t really shown anything new since Moon Embraces the Sun. In his movie Secretly Greatly & drama the Producer, it feels like he portrayed the same character. Btw, has he portrayed a much complex character yet? (Verdict: Only Hit was Moon Embraces the Sun, I don’t understand the hype of MLFTS & the Producers)
Jo Jung Suk, well definitely he is a theatrical guy. Though he has not done a daring and challenging characters (in drama) as yet but I love how he makes a simple character into an interesting one. Say in Jealousy Incarnate, his acting was a little bit exaggerated but do I have to call it over-acting? NO, it’s called interpretation. I actually loved it and the extra movements actually adds colour to the character. I believe he is one of the actors that can go all out and can be as eccentric and crazy as he can be. That is why I don’t understand why he’s only doing those less promising characters. (Verdict: I love him as an actor but he only played characters similar to characters played by Gong Yoo. I love Oh my Ghost for Entertainment value)
For LJG, he is a top act. I don’t know where he was hiding because I only discovered him in Moon Lovers. For me, his performance in this drama is a masterpiece. His portrayal of subtle yet fierce teen Wangso to growing to be a more complex Wangso to becoming an eccentric and obsessive Gwangjong was phenomenal. I found an actor who I can expect to deliver something new in every project. (Verdict: All hits except My Girl which only good for entertainment value & Hero- thought similar interpretation as Iljimae which is a drama that I love to bits.)

*hit or miss rather*