The game looks lovely (I especially like the background), and the central mechanic is interesting and well done. What more could you ask for?
I think mouse to shoot was a little weird since everything else was keyboard. It made it so that I was switching between spacebar and mouse, which just felt sort of awkward (probably didn't help that I was using a trackpad, haha). I think a keyboard key for shooting would work better. It probably also feels better with a controller, which it looks like you already support.
Other than that though, I haven't got much in terms of feedback. Game was a little difficult to me, but it didn't feel unfair at all; I think it's just because I stink at games. I think this mechanic would be awesome to expand. Great work!