A few things. I think the look speed needs to be dialed down a bit. It could be pretty easy to get motion sickness.
I probably wouldn't use copyrighted music in a game. Not that I particularly mind, but it just limits your audience since at some point ID would have to go after you with a team of lawyers.
It wasn't clear to me that the sphere things are projectiles from the enemies.
I also think I would have like to see some new kind of gameplay aside from the standard first person shooter.