Fun game, well done to you both! I would personally recommend a short delay after a target is successully hit before it allowed to be hit again - I found the best tactic without the delay was to build up a large stash of 'ammo' and then find a lone static target and spam away on top of them.
Additionally, playing a second time I discovered a couple of bugs - I started off already on 30/30 targets, and when moving too far away from the spawn point the music and sound effects both fade away compeltely.