very impressed this was done by scratch i've got a couple of ideas on how you could make this fit the theme a bit more
for a start you could have the player able to move left and right and have the gun be able to aim up and down - this already makes for some more interesting things (like sky ghosts!)
secondly you could have the player have a limited amount of ammo and have to go back to a house to get more - but the enemies would still follow him
thirdly since this game isn't topdown to make it more chaotic you could layers enemies behind eachother - changing their alpha to a bit less so it looks like there in the background then make it so the player can walk back and forward to shoot the enemies