I think this demo is very fun and I hope to see more in the future. As far as I could tell, the level design was fairly balanced and I never found myself getting frustrated, despite all the times I died. I also enjoyed the music, it fit the game's theme.
Suggestions*
-A ability to replay what you did in real time after you beat the mission.
-A point system
My only problems with it is that the grenades didn't feel like they had much of a use. They where cool to have but I found my self only really using the guns. The throw and pickup buttons where also a little off putting, because you had to take a finger off the wasd keys to use them.