What I love about this is game is the visuals those are awesome you really make a tremendous job right there :) Gui & Character & Movie like style just plain awesome
What I think you could work on:
1. Gun could do more to enemies like indication of damage and some effect when the die would give more satisfaction to the player
2. You should be able to crouch and shoot
3. You have some minor bugs with stairs
4. Enemies AI could have more if's ;]
Awesome work !