I'm impressed!
I love the 3D feel to this game. I also love the ease of use of the weapon... great auto fire, great reload feature, great controls. Great idea of pressing shift to move, rather than having to click or something. Nice power-ups, nice ability to manipulate backgrounds (like blowing up coke machine, boxes, etc). Good enemies, and I like the way they move and shoot.
It's also reasonably difficult, but not too much. It's a really fun game, and I can see this being a FANTASTIC game if you make the full version. You've got feedback now, so DO NOT SUBMIT ANY MORE DEMOS. Seriously, I need to see the full game. It's itching me now, and I can imagine that as long as you put effort into it, and keep working for a couple of months or so, you can make this a full version. I'd ideally like to see a long game with multiple types of enemies, and weapons - but just do your best to produce whatever you can.
This is a great game idea.