I had some trouble getting into your game in the beginning, because I didn't understand the controls properly and I was clueless on what to do. Then I got it and got hooked, the really cool design and the atmospheric music add a lot to the whole feeling.
I hope you will continue working on this game and include some more power-ups and maybe a bit of story to read in some of the empty rooms about what happened and where exactly the player is.
Control issue: if you stand really close to a wall that's north of you and try to shoot left or right it's like the shot gets stuck in the wall and doesn't fly towards the enemy. Cost me some lifes :D