Wow, so many opinions here I disagree with :) but here's my unpopular opinion:
Foreigners in kdrama are just plain awful.
They are mostly western people, speaking a bit strange english accent (probably because they don't use english often since they live in korea). It's really off-putting and breaks the illusion.
Also the foreigners usually have boring roles, like generic businessman that simply says "thank you for the business deal we just made!"
They also over-act and make it look silly.
But the worst is when the korean actors have to talk english back, and the accent is so broken you can barely understand what they're saying.
Also every time a foreigner enters the scene the atmosphere somewhat changes and the focus is on the foreigner, even if he has no special role in the series. I don't know what it is, but do they think it's cool to have a foreigner in their series?
I'm not a Robot has pretty much everything of those type of scenes. Love the series but the foreigners in it are just awful.
There are a few series that manage to do it properly, like:
- Mr. Sunshine
- Descendants of the Sun
- Crash landing on you (switzerland scenes)