Hello! I was one of the streamers who took part in Feedback Quest, and I'm here to leave some comments I had while playing.
The tension through the music build up was nice. It does break a little at 7 runes when the song plays in full and fades out before looping, but that should be an easy fix. I also enjoyed the silliness of the game, including getting to shoot Slenderman in the crotch.
That said, there was no threat in this game. Slenderman's "hands" did nothing to me, nor did touching Slendy. Meanwhile, the game became a little aggravating to play when finding the runes due to how little you can see forward and a lack of anything to give you an idea where you are. I know the original Slenderman was like this too, but without a threat of losing it just makes things tedious. I also found the "jumpscare" sound when you got close to Slenderman dull.
That said, I do think you have a good sense for building tension as proving with the use of music. With that in mind, I think you should collaborate with the developer of "While you sleep I hunt ghosts with the pope's revolver." That game has no real tension, but has good mechanics and comedy. I think bringing in some real tension to work off the comedy would be a cool idea. But that's me.