I like the concept! Took me a couple rounds to figure out what to do (the floating cork at the top helped a lot). I did find the controls tricky sometimes when I was trying to cork the gun.
Also, it wasn't clear till after I read the game page again that I needed to defend the houses.
I also liked the split screen part. Wonder if it would be possible to somehow indicate how far down you currently are from the surface. Maybe a gradient on the color of the tiles?