Would it work to add before the AGAIN, HARD, GOOD, and EASY buttons arrows of some kind as a visual reminder of which way to swipe?
AGAIN 
HARD 
GOOD 
EASY
If it wouldn’t be too confusing, I think it would be helpful to have a quick reference reminder of which way to swipe. (Assuming the appropriate adjustments to settings are made.) Obviously you would want to use a different arrow graphic so it doesn’t look like a PLAY button.
Thank you for your consideration!