I speak very, very basic Korean, learnt from another source. When Duo announced the update that brought the Korean learning, I, wanting to learn more Korean, instantly started it. However, from my knowledge of Korean, the Hangul (alphabet) lessons could be improved. As of now, they're kind of difficult, and taught as whole words opposed to letters. This is only a suggestion - the course is great as far as I've got - but Hangul should be taught by consonants and vowels separately, how to say and use them, and what 'syllable block' should be used to form the specific word you're looking for. From learning Korean via a different source, I found the method of this (learning it step-by-step, letter-by-letter) much easier to understand, read, and speak the language. ^^
You are echoing thoughts expressed elsewhere in these Forums. Many of us have suggested that folks learn hangul from other sources before starting the course. https://www.duolingo.com/comment/23695875 provides an extensive list of Korean language resources on the web.
https://www.duolingo.com/comment/24887752 is where I am posting my own suggestions for the course, and it might make sense for all of us to post in the same place.
The DL Korean team does welcome and pay attention to suggestions, and the course has already improved significantly from when it first appeared, so we all hope you will keep the suggestions coming.