Very creative! That was unexpectedly too fun! Very easy to play and has a saving system (still on wave 11 here). I have some suggestions that crossed my mind. Don't need to take them by heart, they are just ideas:
- How about change the color of the square after the Fairy pass through it (for example, desaturated orange) and play a subtle sound effect?
- In some waves, I lost track of the next square and didn't know where was the next one. It didn't happen often, but when it did, I ended up losing. How about making a pointer arrow to show the player where the next square is when the player strays away too much from it?
- Should the player immediately lose when a single square is missed? The game could be a little bit more forgiving, allowing the player to miss at least one or two, before losing.
- Besides squares, more geometric shapes could be used, to diversify and bring engagement (the tenth wave was hypnotic!). But maybe this doesn't need to be mentioned as I consider it to be an extra polish.
- (Edit) Also, when a lot of squares are aligned, how about making the colors of the far away squares less relevant, for example, by minimizing their neon effect (or desaturating them)? I don't know, maybe something to hint to the player that the square ahead should have the highest priority.
That's about it. Very promising game!