Goo Joon Pyo
For one thing, Joon Pyo strikes me as much more, erm, sexual being than the JDrama's Domyouji. He comes off as much more physical and flirtatious. No more promiscuous than his Japanese counterpart, but definitely more aware of sex and his own sex appeal. Domyouji just seemed completely insulated against sexuality for the most part, even when it came to Makino. I think a good example of this difference was in the different ways Joon Pyo and Domyouji reacted when they found out their henchman had planned to rape Jan Di/Makino. In the case of Joon Pyo, he clearly understood the full implications of their plot, and got very, very angry with them. Domyouji, on the other hand, seemed much more dismissive of it--like he didn't quite understand the full implications.
Then again, I may be misremembering, I'd be very interested to hear the impressions that others have gotten. What differences, in general, have you noticed between Joon Pyo and Domyouji so far? Do you like them? Do you dislike them?