Nice little game you got here, I liked the mechanic with all the different guns gave it a feel of making some progression. The final boss fight was also a really nice surprise so great job on that!
I found myself getting hit by the scorpions quicker than I could react to them, since they moved so fast and the camera is so close, would also be nice to have a few more sound effects to give the game more meat, things like enemies dying and attacking would go a long way.
Great job!