Funnily enough, the game gets easier as more enemies appear x)
Once you get into the rythm of doing :
3 shots -> Stomp -> 3 shots -> Stomp while staying still, you become basically immortal since the ennemies don't have enough time to reach you before your next stomp ^v^
Having more types of enemies would get rid of that issue so i wouldn't pay too much attention to it!
Other than that i really like the sounds you've chosen for the game ! Stomping right in the middle of a huge crowd of enemies feels great, and the sounds only enhance that further !
Good game ! Just needs more content ^v^