Nice! I like the art style and atmosphere, the reaper feels scary and its sprite conveys its intension well. I like how both the ammo respawning and the reaper chasing you force you to move around.
Because the ammo always spawns in the same place and both the reaper and ghosts follow you at the same way, the best strategy I found was to move around in circles across the arena, so maybe try adding other enemy behaviours or more incentive to move in different ways.
Also, the enemies spawn very slowly at the start of the game, and then start spawning exponentially faster, so for a lot of the game there are little to no enemies, and then they spawn in one big boom, see if you can make them spawn a little more gradually.
I liked the UI for the ammo amount, and the animation for reloading. The sound for dying is funny.
Cool game, well done.