Off to an awesome start! Guns feel good to use, enemies are fun to shoot, and the levels look great. I really like the atmosphere so far. My immediate concerns are the input issue that Hakita mentioned as well as ranged enemies. The game seems to run smoothly when I'm standing still and moving forward, but whenever I move the mouse to look around, it becomes jittery. I have mouse sensitivity at maximum and I still can't turn as fast as I'd like; this might be related to the first problem that Hakita described, however.
I understand the design philosophy of making hitscan ranged enemies that will hit the player 100% of the time with line of sight, as classic games did do that. I disagree that modern games should still have them - DUSK and Amid Evil do just fine without it, and the ranged enemies in those games are still a threat. When you walk into a room and see zombie gunmen in the middle of several melee zombies it's tedious, because you immediately have to move *backwards* instead of *forwards*. Moving towards the enemies is fun and encourages you to strafe around and use the combat arena of a room. Moving backwards encourages you to lure enemies into a chokepoint and pick them off as they come through, then play "peekaboo" with the ranged zombies until you finish them off, which isn't as much fun. You can't play aggressively in Hell Hunt without getting shot several times and losing a lot of your health, especially on Hard mode.
If you intend on keeping the ranged enemies as they are in Hell Hunt, I strongly suggest making them A) shoot less often, and B) give them a delay on how fast they shoot when they spot the player. If they see the player, make sure they can't shoot for at least a second or two so the player has time to find cover. I took a lot of damage in this demo that couldn't be avoided because I couldn't react fast enough and didn't know where the ranged zombies were, which did not feel fair.
With all that said, Hell Hunt is showing a lot of promise already, and I love the sound design especially - those pistols are awesome! With some more polish on the control input and a change to make ranged enemies less tedious, this could be really great. Keep up the good work!