I had a lot of fun with the demo. I love the suspense of turning a corner not knowing what will be lurking there.
However, I would like to suggest adding a couple of things. First of all, have you considered adding windows to some of the rooms, which could allow you to peer through and see a small portion of the room? You could really up the suspense, I think, by allowing the player to see a few of the many creatures lurking in a particularly dangerous room. Perhaps the cone of vision through the window would be really small.
It would also give players a little more of the information they need to decide whether to make a go at that particular room now, or wait and come back when they find better weapons or have more health.
Also, I'd consider adding something like what Anna Anthropy talks about in this article:http://www.auntiepixelante.com/?p=1319
Specifically, Anthropy talks about how in AD&D: Cloudy Mountain, players are often given audible and visual cues that inform them of nearby dangers. I think you could do something like this to great effect. Hissing noises, groans and growls could inform you that creatures are near, and each creature could have a distinct sound.
Also, imagine how cool it would be for the player to encounter a half-eaten human corpse, and know that some really frightening creature (perhaps something you rarely encounter that deals a ton of damage and takes a ton of hits to kill) must be nearby.
Anyway, just thought I'd share a couple of ideas with you. Really like the game, and I'm looking forward to seeing how it progresses.