Yes, I would definitely recommend cycling in South Korea. I still prefer Japan, but I enjoyed South Korea as well. What is so good about it?First of all it is a very safe country again. There is no apparent crime, people are very friendly and I have always felt safe, even when free camping. There are hardly any tourists in South Korea and therefore no tourism-related crimes or scams. Traffic was not too bad either although I felt safer in Japan, but South Korean drivers are usually very polite, too. Unfortunately, some roads have poles in the middle to separate the lanes and cycling here feels incredibly dangerous because drivers cannot move over to the other lane to pass you. But luckily we did not encounter too many of those roads.
Like in Japan there is so much to see: Temples, caves, beaches and folk villages - and almost everything is rather pittoresque. Again, we took loads of pictures because everything was so interesting. I did not know much about Korean history but I was fascinated about what I found out. From the 6th century kingdoms of Silla to Japanese occupation and the separation into South and North Korea there was so much I had not had a clue before. South Korea is worth visiting in order to learn about its history alone! South Korea is a rather small country making it an ideal destination for a 2 or 3 week bike holiday. It offers enough to keep you busy (we spent 6 weeks in Korea), but you could get a complete overview in a relatively short period of time.
I especially enjoyed the food - because here in Korea we could at least afford it! Barbecues, Kimchi in all variations and fantastic Western-style cakes - we ate in luxury. South Korea is not a very cheap country for Asian standards, but a lot cheaper than Europe or Japan and travelling with a bit of luxury was no big strain on our budget. We usually ate out once a day and stayed in hotels half of the time.
When cycling in Korea keep in mind that the gradients can be brutal and the humid climate torture - plan your mileage accordingly. I was always wearing a cheap little wet towel around my neck to wipe off the sweat. Maps of Korea in English can be found everywhere, but do not rely on them - they are usually not very accurate. Various times we were looking for roads that only existed on our map but not in reality. But as Korea has a good road system you can usually find an easy way around it.