Good demo, I had fun with it. What engine did you use for it? is it a doom mod or something? As for feedback:
> Guns badly need juice. Give the gun sprites kickback or something, and give them bassy sound effects.
> I think you need more landmarks, like the Christmas lights on that one level. It got quite monotonous looking at the same thing when I was finding my way through the levels.
> The level where the map changes around you is great, really neat level.