Interesting theme adaptation with quite a challenging experience for me (maybe it's my skill issue). By the way, I find it a little bit difficult to control character mid-air, since the character moves super fast from one position to another and the gun rotation could be changed entirely (according to mouse position) during that period. Some helping mechanics should make the game a little bit more forgiving, for example; Slow-mo, Gun direction UI indicator. Anyway, an enjoyable entry for this jam!

Nice game! Has potentoal to be casual mobile game too. You can welcome speedruns here just by adding a timer. I can finish a level quickly by jumping directly to the exit if I'm skillful enough to click on the right angles at the right time.
About the hold fire for higher jump, I think it doesn't work. I just got lucky to pass that level by spamming clicks. Repeatedly dying until it sent me to the flag while spinning. Haha!
Suggestion: Add a short line that indicates the aim angle. That way player can easily visualize the trajectory of the next shot.

Quite an easy game overall as you can chain gunfire from the start and a lot of the levels become trivial after you master this. you could've added an obstacle like spikes or enemies (equivalent to your world) or something to ensure players can't just fire straight to the goal. Adding spikes or something around the level to subtly direct the player. 

I enjoyed it though as the mechanic is pretty fun to mess around with!