I have played your game, I have quite enjoyed the concept. I like the light is a weapon. But I had trouble figuring out the controls. The movement and using the flashlight were quite intuitive. But I have not a find a way to use the key, I was standing right besides the gate and was trying all of the keys, but nothing happened. I also do not know if I should find more than one key, but I explored a lot of the map, but did not find anymore. If there are more keys, do they spawn like diamonds and batteries or are they spawned in the beginning like the first one?
The other thing I did not quite get is spawning of the items. If I guess correctly it is connected to killing the enemies, but they always spawned at seemingly random place near the player. And because I did not find a way to progress in the game, I found that stacking the diamonds a lot on each other is more white color than lit environment.
I would suggest making a legend that will explain the controls and maybe add a way to close the game without Alt+F4. But again, I think the game could be really great, the part I could play was entertaining even without a goal.