I guess the answer is "it depends." As an American, I wouldn't recommend for a friend to go out of his way to fly halfway around the world just to climb Hallasan. But if he happened to be in or near Korea anyway or were planning a trip to Korea anyway, I'd definitely recommend going to Jeju to climb Hallasan in combination with seeing the other natural sights on Jeju. And if you're going to Jeju anyway, all the other natural sites can be seen in a day, so as long as you have a second day, you aren't losing much by climbing Hallasan -- unless you prefer to see all the tacky made-for-tourist junk there like the Ripleys museum. With 5 nights in SK, Jeju/Hallasan appealed to me more than most of the other major tourist destinations in the country, and I'm glad I chose to go to Jeju over Busan or Gyeongju, neither of which interested me very much.

I have tons, but haven't post-processed them yet. Anything in particular you want to see; let me know and I can email/post. I didn't feel that it would be helpful to post SK pics because there are tons of photos online of all the sites I write about (this trip wasn't exactly uncommon ground), and you can Google Image search for stock images of most of these places.