Nice submission! I found it to be a more of a test of my internal metronome than my reflexes, but it was a nice challenge nonetheless. There are many opportunities for improving this with sound design, and I think the other suggestions here would push it in the right direction. But as-is, it’s functional and well-executed. The only thing I’m really noticing is how it might be helpful to announce the speed aloud when the text changes on the bottom of the screen (but it’s sort of obvious once things get moving).
If I had to do it, I would probably have a synth for each enemy, which has some modulation and filtering to it that intensifies as they circle around you and enter your crosshairs. Maybe make it musical and change it up every round with different scales or chords? But there’s really no wrong way to do it—they could be fighter jets against your anti-aircraft gun or bleeps against your bloops too.
Something else I might consider is the left and right controls applying some thrust rather than abruptly changing velocity. Imagine trying to match their speeds instead of finding the perfect timing? It would fundamentally change the game, but could be a fun experiment?