Good basic idea. Halfway there.
There is some really cool stuff in here, but it needs work. I'm just going to list a bunch of stuff that I think could make this really good:
-Firstly, it's waaay too easy.
-Thinner outlines on things, a shading style that better conveys shape, and anything else that will make this look like a bunch of flat layers.
-Fix the clipping. Twice I got hit by those rock traps when the character was clear of them (or so close that it was reasonable to assume that he wouldn't be squished).
-Limited ammo and the need to collect it (maybe stripping it off commrades bodies).
-The flying level was a cool idea, but just needs more work all around.