You've got a base for a game here, but not much else yet. I'm keeping in mind that this is a prototype, and you're already aware there's a lot to be done. The design of the level itself is actually quite nice, and I'd say it's the best part of what you've got done so far. The menu options and the instruction text need to be drastically downscaled to a smaller size, as does the actual HUD when in game. If you have HUD elements overlapping, that's a sure sign that they need to be rethought. The guns look nice enough, and I won't speak much on the combat as it's obviously very in progress.
The major thing about this prototype that is a big no for me is the mouse look. I can't tell if it's the sensitivity or the speed, but it feels very off. Almost as if every movement you make with the mouse is getting dumbed down and slowed. Definitely something to think about.
I look forward to seeing improvements! :)