This is a great set up! I'm enjoying it. I like the words and phrases you picked and the order of introduction. My hopes for future updates:
Option to reverse the questions: show the English word and user must choose correct Korean word.
Option to quiz on sound only or word only so we can improve weaknesses in listening or reading. When both are present it can be a crutch.
More examples where the past/present/future tense changes and we have to pick the right one. I'm learning quicker from your game in that aspect than I am a textbook or other methods, how cool!
The leveling up is a little too fast in my opinion. I think we need to get the words correct more times but I'm also unsure how easy that is to integrate.