First off, I gotta say the atmosphere is on point. The amazing color direction really sells how threatening the monster is meant to be, which also makes the switch in power when you get the gun very satisfying.
That being said, the games loses a little of its charm once you start understanding the systems that are in place. The monster moving on a fixed pattern without any wiggle room made it feel less scary. Also, the lack of a clear indicator on the enemy's vision radius made it feel somewhat unfair when the players gets spotted by a turret that doesn't look like it should have seen you.
There's also a lot of missed potential on what happens after getting the gun. I expected the game to be really serious about only having one shot to kill the beast, but since it moved so slowly and you could usually kill it from a distance, there wasn't enough of a chance for me to miss for that possibility to actually be worrying. Maybe it would be interesting if the monster became faster or changed its pattern once the player got the gun.
Overall, I think the premise has a lot of potential, I hope you keep working on it once the jam is over. Good luck!