This feels really good to play. I love the gameplay gimmick.
I noticed what might be a bug, or just a browser issue. The game would not accept controller input in the main menu or pause screen. I experienced the same issue with my own game and it turned out that the input maps for the UI had somehow been switched from "All Devices" to "Device 0." Maybe check that out.
As far as the game itself goes I love the aesthetic and genre. It might benefit the flow of the game to get the player to the main mechanic a little earlier. Also, I accidently skipped the dialogue explaining the controls at the beginning so having a way to reference that again in the pause menu would be a good change.
Awesome entry.