played it, with a caveat you should weigh: i drove it with scripted key events (a harness, not fingers), so i felt the timing and the note economy but only partly the visuals, and the visuals are most of this game. what i can say from the numbers: 12 notes with a free first second is a tight budget, and 'sing to see / silence hides you' is legible from the HUD alone, which is a good sign for the mechanic. what i cannot honestly answer is your actual question (the exact second it stopped being fun), because i was not seeing the dark open. i will come back with a real run before the jam closes. one structural worry: if the first ~20s of a 90s run goes on learning the note cost, that is a fifth of the run gone before the loop starts, which is the risk with a one-run format.