It's pretty good but it lacks one visual communication to the player. The pickable rocks doesn't shine or at least pop out more than the others, as this will help the player on finding them. The turret bullets go through wall. 

Starting the game wastes a bullet (clicking start meaning the game thinks that you're shooting even when you're not in the game yet), fixed this in my own game by checking whether the main menu is instanced then you can shoot, though the ammo counter is pretty misleading since I thought that ammunition is apparently limited in the game and you have to pick up replenishables. Add that in the instruction menu or something? 

Audio is pretty good. Graphics is good-looking, and alien enough.