I stayed at the Ramada Plaza Jeju over the Christmas holidays and it was fairly comfortable. Although there are some good points, the biggest problems are the stuffy, hot rooms and the crowded parking lot.
First, the good things. The hotel lobby and surroundings are impressive. The winter decorations were excellent. There was a charming winter market going on in the evenings. Check-in was problem-free, except that the underground parking lot was quite crowded (you'll probably want a car when visiting Jeju). It was kind of a pain finding a parking spot.
Staff throughout the hotel was friendly. We used the concierge a couple of times and they were helpful.
The room with the double beds was an acceptable size and seemed clean. There were no problems with housekeeping. The beds were comfortable. The free water bottles and small refrigerator were handy. The TV had some foreign channels, which I appreciated. Soundproofing was just average. The furniture was comfortable.
Unfortunately, the room was extremely hot, which made it difficult to fall asleep. There is only central heating, and in the wintertime you (or the hotel) cannot turn on the air conditioning. After I complained, they sent up a rotating fan, which helped somewhat. However, the room was still quite uncomfortable. Opening the windows helped slightly, but then of course there was noise from the roads. This is a big problem that the hotel needs to fix!
The bathroom was ok. The shower feels slightly cramped when it is closed, but there is also a bathtub. I think that there should be more space around the sink for your things, as there is not much room. The lotion and shampoo and others were good however.
The breakfast buffet was pretty good. It had a nice mix of Korean and other cuisine. Although the menu mostly stayed the same everyday, most of it was pretty tasty. I enjoyed the coffee. The buffet dinner they offered was pricy but pretty good as well. The lamb was great, the sushi not bad. Decent dessert as well. The place gets pretty crowded so just be aware of that.
Check-out on the last day was very easy. Overall, it was a good stay, but if it was wintertime, I would not come back here, as the rooms were very hot and stuffy, which prevented a good nights sleep.