Dude exactly! I just had my wife sit in front of the monitor while I played and she had the headphones on and watching. Her comments were as follows:
"Ok this is making my stomach hurt I'm so anxious cause I know it's obviously going to scare me."
"Can your flashlight ever go out?"
"There's the first note....grab it! Wait...why is it making that noise?"
LOUD DISTORTED NOISE
"OH MY GOD BABE WHAT IS THAT?!??" <takes headphones off> "I can't do this. Seriously I can't. Who would want to play something like this?"
It's this exact response that would get people playing left and right. You nailed it by saying you don't need fancy graphics. It's the simple concept of sight and sound that makes this quite the psychological thriller.