I'll start by saying that the sound design is really good for the mood you're trying to evoke. It did a lot of the legwork of setting up a tense environment.
However, I think the incredibly slow walking speed and large map downplayed the tension a bit; for me at least, tension devolved into tedium. Tension is generally hard to hold, and ambling around a massive building made the tension slowly fade away, because nothing really changed. There were a couple of (very cool) strange things flashing momentarily on the screen, which did serve to add a bit of tension, but there would inevitably be long stretches where I'm backtracking because I got lost or where there just weren't any events triggering. I think the lack of variety in the building also didn't help this, as it facilitated getting lost.
I liked the flashlight having a forward arc, as it made me often question whether something was sneaking up on me (though sadly that didn't seem to happen).
Overall, a strong start that, for me, didn't manage to carry through to the end. You did manage to make a 2D game that made me feel tense for a while though, and 2D horror is very difficult to pull off, I think, so well done on managing that.