I was in Jeju last year and it seemed like 50% of the people there are from other parts of Korea, and do not speak 제주도 사투리, those that did use the dialect understood me just fine when I spoke 표준말 to them. It seemed to me that most (not all) of the nouns were the same, so the largest differences I noticed were in the final verb form. The only problem I had communicating in Korean in Jeju was when I greeted a couple in the elevator of the hotel... and they turned out to be Japanese.
Jeju -- I just had to go see it because everyone praised its beauty. I wanted to climb 한라산 because that scene from 내 이름은 김삼순 drama had been stuck in my head. But what did I think of the REAL Jeju? It was overpriced, but I suppose being a California native I have no right to complain about other places being too expensive; however. as a California native I found the scenery a bit mediocre, a far cry from the 'breathtaking beauty' I had heard so much about. It was not much different from our Catalina Island on a clear day, also we have a thing out here called "the west coast" with scattered beaches that span the three states along the western border of our nation .. so... I guess I'm hard to impress when it comes to coastline.
Those stone statues that remind me of garden gnomes really cracked me up -- I dared not share my impression of these phallic pygmies, perhaps it is just my western side that interprets art in this manner, but alas I could not help but notice that their heads looked a wee bit circumcised.