There is an interesting language classification by CIA in the US. CIA classified Korean, Japanese, and Chinese as one of the most difficult languages for English speakers to learn. It seems that English speakers face similar level of difficulties in learning those languages, although Chinese are very different language from the other two.
So, I think that the difficulty that you will face would be similar to the amount that you faced when you learned Chinese (I believe that you are a native English speaker based on your profile).
There are different kinds of difficulties known.
1. grammar : Chinese is the easiest.
Korean and Japanese are more difficult
2. writing system: Korean is the easiest.
Chinese and Japanese are difficult
3. Pronunciation: Japanese is the easiest
next is Korean (but the gap between Japanese is not big)
Chinese is the most difficult
Although those different kind of difficulties, It seems that the overall difficulty to English speakers is in a similar level.
Another observation that may help to see the difficulty is Chinese who are learning Korean language. I saw some Chinese, speaking Korean in TV, sometime. Their language achievement looks better than English speakers who are learning Korean. There are a lot of vocabulary with the common root, so Chinese speakers (or anyone who learned Chinese) can take advantage in learning vocabulary.