I used Shanghai, Hong Kong, Tokyo and Beijing as examples because they are all destinations in their own right-at least that's what I read. Seoul and Busan, on the other hand, doesn't give me that feel when I read about them. Initially, I was planning this May to do a trip to China and Japan-then I thought of adding South Korea onto the trip. To be honest, I only want to go there if the general consensus turns out to be that Seoul and Busan merit trips in their right as the other places I mentioned do. That's why I commenced the thread. You guys have been helpful nonetheless...

I've been to all those cities too. The problem with S Korea is it has no "big draw card" to motivate tourists to fly all the way over there. Even what they have is not well presented. Take Tumuli Park (Gyeongju) and the surrounding tomb-mound as an example. The park is bland compared to China/Japan standards. The mound itself is not big enough draw to attract tourists. After you've seen the third one, it all start looking the same. They should at least make the surrounding area better. The city Gyeongju is not very interesting.
If you are adding SK to your itinerary because you're going to China and Japan anyway then that's a good decision. I did exactly that. However, if you have 2 weeks of vacation a year and you're flying out across the globe to visit one country, SK wouldn't be my choice. All in all, I enjoyed my time there. It complements China and Japan very well because all these 3 have historical ties.