I'm not sure if the intention was for a horror game, but the claustrophobic darkness and the jump scare of turning around to see the enemy does a great job of creating a horror atmosphere.
Some kind of hints signposting where the player should be going, even very subtle ones, would be very helpful, as would some way of indicating paths the player has already taken. Currently it seems impossible to navigate by anything other than trial and error, and with no memorable visual features I think I kept running round in circles (although I couldn't tell!) I was randomly running around the maze for a very long time before I found a single key, so I think the maze might be far too big (again, I couldn't tell as I could just have been repeating the same steps over and over again!) It also feels very cheap when the monster sneaks up on you with no warning - perhaps if the monster made a sound, getting louder as it gets near, the player might have a better chance of avoiding it. Perhaps the battery should recharge too as running out is basically game over.