It seems that it was not clear to the user how many times the player has been penalized since it only shows the screen darkens. He suggests to have a health bar or some clear instructions to let the player know how many times the player can miss the beat before the game ends.
For the beat detector (where the red box goes to the white box), it seems that it was not clear to the user since you need to hit the beat perfectly. He suggests to have more flexibility where you can land a "good", "great", and "Perfect" when the beat is hit. Otherwise, you need to land perfectly on beat or else you will be penalized.
Based on Jon's Feedback:
It seems that it was not clear to the user how many times the player has been penalized since it only shows the screen darkens. He suggests to have a health bar or some clear instructions to let the player know how many times the player can miss the beat before the game ends.
For the beat detector (where the red box goes to the white box), it seems that it was not clear to the user since you need to hit the beat perfectly. He suggests to have more flexibility where you can land a "good", "great", and "Perfect" when the beat is hit. Otherwise, you need to land perfectly on beat or else you will be penalized.