Got a high score of 310.
It's a nice idea, and the execution is roughly decent. The projectile speed is good enough.
Few suggestions that I can think of are-
1. Each time the projectile colour changes, set that colour to the crosshair as well. This way the player won't need to constantly look back down every second or two.
2. Display the feedback sooner when a target is hit.
3. Since the main gameplay is occurring at the top of the screen, that's where the attention is, and thus, you could experiment with the health UI to make it appear somewhere on the top of the screen, perhaps as part of the rotating thing. (You could also see how the health UI looks if it is in circular shape, if you put it on top of the rotator)
Nice work, and good luck!