On the surface, with all the technology that surrounds you in Korea you might be mistaken for believing that it is a fully developed country but you'd be terribly wrong. Don't forget that Korea has only enjoyed material wealth in Western terms since the late 80's. Most Koreans over 20 years of age still think like provincial peasants, even in Seoul.
Be warned that although Seoul has all the physical attributes of a major capital city it has almost none of the more important aspects. The ones that really MAKE a capital city, a world city..... being cosmopolitan, outward looking, international, diverse, knowing any other language but Korean, having a real buzz and ambience of a world city.............you will find none of this in Seoul.
I can honestly say that Seoul is the most clinically boring, grey, uneventful, closed-minded and xenophobic Asian capital city of the 10-odd I've been to.
My advice, avoid Seoul unless you like:
a) Not being able to communicate with anyone in English (or any other international language for that matter)
b) Being stared at if you are not Korean (believe me that Koreans stare at caucasians, South-East Asians, Africans and even the Japanese.) Basically if you are not fully 100% in-bred Korean and speak Korean you will be stared and pointed at.
c) No diversity, no colour, no ambience, no culture except Korean culture.
As I said, Korea is materially wealthy but culturally so poor, it's quite unbelievable.
This is more advice than anything. Although the number of foreigners is steadily increasing, Koreans may still gawk and stare at foreigners. The only part of Seoul where you may be received without a blink is ITAEWON, where the American Army Base is. Don't take the staring personally as Korea is still a homogenous society--it becomes even more pronounced outside of Seoul.