I think the name of the game here in terms of improvements is feedback:
Some sort of sound or reorganization of the ammo HUD is needed, it's hard to tell when I need to reload there. Some sort of dry fire or click when you're out of bullets would help.
In general with the HUD I'd assume it's placeholder but you've got a lot of unused space, you could at least move the ammo counter/what gun you have widget over to the right hand side.
Add some randomization of pitch to the gun sounds too.
The tilt is fine but it needs to occur when you're strafing, not when you're turning.
When running over pickups the popups happens way too fast, I can't see what the text said. Either make it last a few seconds longer or have it up on the screen itself.
Lastly there doesn't seem to be much of an incentive to kill enemies. It's one thing if they're easy enough to avoid, but they don't seem to impede my progress to the next area nor do they seem to drop anything I'll need.