Some ideas that would have made it even more fun for me, though which might change the game too much from your original vision:
Ghost arrow: show what shot I played last time, so I can tweak my strategy.
Reset: some sort of gesture to quickly go back to the start, so I can tweak based on the ghost arrow.
Escape velocity: a fun part of orbital mechanics, and a way to penalize me for just using a “hit as hard as I can” strategy where the only changes I make are shot direction.
Hard mode was the most fun because getting a cool hole-in-one felt really fun. I almost missed that hard mode was even an option — the help screen says “hard mode” so I assumed that was the mode I was in, but it turns out it was the button to play in hard mode, which turned out to be a lot more fun because of the reset mechanic.