How did the natives treat you? - See above, if you want further information feel free to respond with a more specific question.
Korea is a very, very easy country to live in without knowing Korean.
Korea has way more English, from my experiences in Tokyo and Osaka, than Japan does.
Things are a lot easier as you'd expect due to knowing a conversational level of Korean though. Although living would generally by manageable as Korean English listening skills are actually pretty good.
Korea is brutal towards anyone who isn't a size 0 basically. Advertisements for diets and losing weight are everywhere. Basically if you have an ounce of fat you're considered disgusting and should do something about it. There are an increasing number of overweight people in Korea though but the fashion industry continues to not cater towards them and so many have to buy their clothes online. Korean plastic surgery results in basically every Korean model looking identical.
See:
http://imgur.com/gallery/0MMzzLQMiss Korea 2013 candidates = look similar to anyone else?
Living in Seoul is a lot more expensive than the rest of the country but if you eat Korean food and drink Korean alcohol it's really not expensive at all. My phone bill is double my gas and electric put together.
My outgoings for a month are usually somewhere along the lines of 500-600,000 won which is about 350gbp (rent is free).