Very unusual game! Reminded me of old-style arcade games I played in my childhood. The hidden object layer added an interesting mechanical twist, too.
Overall, a very cool idea that has a lot of potential. My only criticism would be that combat is not very exciting as it is, you just click the guy till he's dead, and that's it. And they're hell of a bullet sponges too, for no particular reason. I think it would be more interesting if enemies had a lot less HP, but instead moved around, popped in and out from obstacles, or moved towards you. It would have added a lot more variety and made gameplay much more dynamic.