The concept is really good. However, I'm a bit frustrated about the fact that once we lose the gun, we basically have to suicide (cuz I'm a noob, lol) - maybe enabling the restart feature or auto restart would be good, otherwise, maybe you could find a way to give the gun back to the player. Like others have said, dragging two of the same items creating the next tier version would be a nice touch. Random power-ups to be collected would be a great thing as well. Other than that, an improved UI like the box on the right side along with a confirmation button will make the game seems more polished; often that I misplaced the gear because of the auto-attached features. The gameplay is sold and above all, it's a great concept and I like it. Great job!