I downloaded your game and gave it a whirl.
And i really like this.
Everything ran smoothly and was really easy to pick up and play without instructions.
The only thing i felt was lacking was the sound effects and possibly some music to help generate some more atmosphere.
I contemplated writing something similar a while ago, more along the lines of the 'Ishar' games but instead decided against the step movement idea.
But it works really well in your game.
I can see this working really well on mobile devices.
Might be worth considering porting it to mobiles when you've finished the PC version.
The graphics have a real old school charm about them.
Keep up the good work.
KJM