I definitely agree with a lot of the reviews here that this is an absolutely incredible game! Especially given the time constraints.
The visual style is simple but charming, the mechanics are intricate yet understandable and the overall presentation is wonderful. It's definitely difficult enough and the included option to change the echo speed is the exact kind of attention to detail that shows a lot of care and thought was put into this project.
I normally try to give critiques but honestly I'm struggling to come up with any as this game is just so well put together. I think if you added more levels and mechanics you would have a game worth paying money for!