Alright, here's my thoughts on the demo.
You did a great job on the atmosphere, it all comes together well to make the player keep on his toes. Puzzles were also good. I do suggest you put hints though, it took me a while to find where the books were meant to go.
That said, I was horribly disappointed on the battles, it's too easy to die, you get trapped in the corner and it's over, you should be able to dive or something. In addition, the gun was poorly thought out, a small room is suicide, I got tired of running away, and stopping to find I turned the wrong way, and I can fight. The menu should also be on a separate key, I kept opening the damn item menu when I wanted to fire.
I suggest giving: An extra health, different weapons (primarily a shotgun so you don't have to be directly in front of your opponents), moving with a gun (slower though), and being able to turn when you take out your gun.