Korean (letter) is easy. Korean (language) is quite difficult. There are many irregular syntax and postposition. Also, there are many rules for a prolonged sound.
Modern Korean no longer distinguishes a prolonged sound at least in the written form. Virtually all words that cannot be set apart without a prolonged sound have been changed to those that can. For example, a short 이 ("teeth") and a long 이 ("two") are now homonym in most dialects of Korean; the former 이 has many synonyms like 이빨 or 치아 however, so they can be often distinguished without a context.