Good job on the Spanish. Easier than Korean for an English speaker, I presume. Immersion will be the best to get even better.

Korean indeed is probably most similar to Japanese. The grammar with the verb at the end, and the huge attention to formalities (different conjugations depending on how much respect you want to convey) make it quite hard to learn. There is like 80% of form and 20% of actual message in a Korean sentence. Mix in the influence of Chinese in terms of vocabulary, and you got yourself there a nice challenge.

At least, the writing system is very simple...